Oh, if you’re craving something that’s juicy, buttery, and packed with flavor, you’ve got to try this Buttery Roast Beef Sliders with Caramelized Onions Recipe. These little bites are the perfect mix of tender roast beef, ooey-gooey cheese, and sweet caramelized onions, all nestled inside soft Hawaiian slider buns. Trust me, once you take that first dip into the rich au jus, you’re officially hooked.

The image shows a close-up of two stacked sandwiches on a wooden board. Each sandwich has three main layers: the top and bottom are golden brown toasted buns sprinkled with sesame seeds and seasoning, the middle layer is melted light yellow cheese with caramelized onions that are juicy and golden, and there is a layer of thin slices of cooked meat underneath the cheese. Some melted cheese and onions are dripping out from the sides, making the sandwich look rich and full. The background is dark, and the wood texture underneath contrasts with the food. photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I still remember the first time I made these sliders for game day—it was an instant win with everyone! The combo of flavors and textures is unbeatable, and honestly, it’s super fun to assemble and share with friends or family.

Loaded with Flavor: Tender roast beef, sweet caramelized onions, and melty cheeses combine beautifully for every bite.
Perfect for Entertaining: These sliders are ideal for game day, parties, or casual get-togethers—easy to make and crowd-pleasing.
Homemade Touches: From garlic aioli to a rich au jus sauce, every element elevates these sliders beyond the usual.
Comfort Food Made Easy: Despite all the layered flavors, it’s a straightforward recipe that feels like a treat.

Ingredients & Why They Work

Before we get to cooking, let’s chat about the ingredients. Using quality deli roast beef and fresh yellow onions is key—they really make the sliders sing. Hawaiian slider buns are my top pick for their soft, slightly sweet texture that holds up to all the juicy fillings perfectly.

Flat lay of a cluster of 3 large yellow onions, thinly sliced in a small white ceramic bowl, a small white bowl of unsalted butter cubes, a small white bowl with olive oil, a small white bowl of light olive oil, a clean large whole brown egg with uncracked shell, a small white bowl with Dijon mustard, a single fresh garlic clove, a small white bowl of fresh lemon juice, a small white bowl with kosher salt, a small white bowl with brown sugar, a small white bowl with finely shredded mozzarella cheese, a stack of thinly sliced deli roast beef, a neat pile of sliced provolone cheese, a cluster of 12 Hawaiian slider buns halved horizontally, a small white bowl with Worcestershire sauce, a small white bowl with poppy seeds, a small white bowl with white sesame seeds, a small white bowl with garlic powder, a small white bowl with dried minced onion, a small white bowl of freshly cracked black pepper, all arranged symmetrically on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted Butter: Essential for caramelizing the onions gently and for the rich garlic butter sauce that gives the buns their signature buttery crust.
Olive Oil: Helps cook the onions evenly without burning while adding a mild fruity note.
Yellow Onions: Thinly sliced to caramelize slowly, developing a sweet, jammy flavor that balances the savory beef.
Kosher Salt: Perfect for seasoning throughout—the coarse grain helps draw out the onions’ moisture and enhances all flavors.
Brown Sugar: Speeds up the caramelization of onions with a subtle sweetness, making them irresistibly rich.
Beef Broth: Used to deglaze the onion pan and infuse deeper beefy flavor into the caramelized onions and au jus.
Egg Yolk: The base for that luscious homemade garlic aioli, adding creaminess and richness.
Dijon Mustard: Adds a tangy bite to the aioli, balancing the creamy garlic and lemon.
Garlic: Freshly grated for the freshest aroma and punch in your aioli and garlic butter sauce.
Fresh Lemon Juice: Brightens the aioli, keeping the flavors vibrant and fresh.
Light Olive Oil or Neutral Oil: Slowly incorporated into the aioli to create a silky, stable emulsion.
Better than Bouillon Beef Base: A concentrated beef flavor that gives the au jus sauce its rich, savory depth.
Worcestershire Sauce: Works double duty—adding umami to both the au jus and garlic butter sauce.
Hawaiian Slider Buns: Soft, slightly sweet, and the best choice for holding all those juicy ingredients without falling apart.
Deli Roast Beef: Thinly sliced for tenderness, it’s the star protein in these sliders.
Melty Cheese Slices: Provolone, Swiss, or muenster are all fantastic options that melt beautifully over the beef.
Shredded Mozzarella Cheese: Sprinkled on top for that glorious extra gooey melt.
Poppy Seeds & White Sesame Seeds: Added to the garlic butter for a subtle crunch and nutty flavor that coats the slider tops.
Garlic Powder & Dried Minced Onion: Enhance the garlic butter’s savory complexity.
Black Pepper: Freshly cracked, for that little kick of heat in the butter sauce.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

One of the best parts about this Buttery Roast Beef Sliders with Caramelized Onions Recipe is how easy it is to make it your own. Whether you love a gooey extra cheese pull or prefer to keep things simple and speedy, these sliders adapt beautifully to your taste and time constraints.

Cheese Variations: I often swap out the provolone for Swiss or muenster to change up the flavor profile. Each cheese melts differently and brings a unique creaminess that pairs wonderfully with the caramelized onions and roast beef.
Quicker Version: When I’m short on time, I skip the caramelized onions altogether and jazz up plain mayonnaise with the garlic aioli ingredients for a quick spread. It still delivers plenty of flavor and lets you enjoy these sliders in about 30 minutes.
Make-Ahead Tip: Preparing the sliders a day or two before your event is a lifesaver. Assemble everything except the caramelized onions and garlic butter sauce, then add those just before baking. It keeps things fresh and saves precious time on serving day.
Dietary Swaps: If you’d rather avoid raw egg in the aioli, mayonnaise is a perfectly delicious substitute that’s also quicker to throw together. Plus, you can try gluten-free slider buns to make these friendly for more guests.

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A woman's hand is holding a sandwich made with a toasted, golden-brown sesame seed bun, dripping with thick brown gravy. Inside the sandwich, there are multiple layers of soft, thin slices of cooked meat and melted cheese with a creamy texture, visible just under the bun. Below the sandwich, a white bowl filled with rich brown gravy has some gravy dripping down its side onto a dark wooden surface. Behind the bowl, several more sandwiches with the same sesame seed buns, meat, and cheese are stacked, showing their melted cheese and crispy textures. The whole scene is set on a white marbled surface with a blurred dark shirt in the background, capturing the warm, messy, and inviting aspect of the dish. photo taken with an iphone --ar 2:3 --v 7

Step 1: Slowly Caramelize the Onions to Sweet Perfection

Start by melting 2 tablespoons of unsalted butter and 1 tablespoon of olive oil in a large skillet over medium-low heat. Toss in your thinly sliced 3 large yellow onions, along with ½ teaspoon kosher salt and 1 teaspoon brown sugar. The brown sugar speeds things along a bit, encouraging that gorgeous golden-brown color. Stir occasionally and cook low and slow for about 45 minutes until the onions turn deeply golden and jammy. To finish, add 2 tablespoons of beef broth to deglaze the pan, scraping up all those flavorful bits stuck to the bottom — that’s where the magic is! Then set the onions aside and let their sweet, savory aroma fill your kitchen.

Step 2: Whisk Up the Creamy Homemade Garlic Aioli

In a small bowl, whisk together 1 large room-temperature egg yolk, 1 teaspoon Dijon mustard, 1 finely grated or minced garlic clove, and 1 tablespoon fresh lemon juice until smooth. Using an immersion blender or a steady hand with a whisk, slowly drizzle in ½ cup of light olive or neutral oil in a thin stream until the mixture thickens luxuriously into aioli. Season it with kosher salt to taste. This creamy spread adds that luscious tang that complements all the rich flavors. If you’re in a hurry or prefer, simply stir garlic, mustard, lemon, and salt into mayonnaise for a speedier option.

Step 3: Simmer the Savory Au Jus Sauce

In a medium saucepan set to medium heat, melt ¼ cup unsalted butter. Stir in 1 tablespoon Better than Bouillon Beef Base, 2 cups beef broth, and 2 teaspoons Worcestershire sauce. Let everything simmer gently for about 20 minutes until the sauce reduces by half. It will darken and thicken slightly, developing deep, rich flavor for dipping those juicy sliders. Keep it warm on the stove so it’s ready to serve piping hot alongside your finished sliders.

Step 4: Toast the Slider Buns Perfectly

Preheat your oven to 350°F (180℃). Slice 12 Hawaiian slider buns in half horizontally, but don’t separate the tops from the bottoms just yet. Arrange the bottom halves cut-side up on a parchment-lined baking sheet. Lightly brush the tops with melted butter or the garlic aioli you just made, then toast in the oven for 5 minutes until they turn lightly golden and ever so slightly crisp. This helps prevent sogginess and adds buttery flavor that’s simply irresistible.

Step 5: Build Your Flavor-Packed Sliders

Slather a generous layer of garlic aioli over the toasted bottom buns. Then, pile on ½ pound of thinly sliced deli roast beef, aiming for 2 to 3 slices per slider to get that hearty bite. Layer each with 12 slices of your chosen melty cheese—provolone, Swiss, or muenster work beautifully—and sprinkle ½ cup shredded mozzarella cheese on top for an extra blanket of ooey-gooey goodness. Spoon 2 cups of those glorious caramelized onions evenly over each slider, ensuring that sweet-savory contrast in every bite.

Step 6: Top ’Em Off and Glaze with Garlic Butter

Place the top halves of your slider buns over the assembled ingredients, gently pressing down. In a small bowl, mix 6 tablespoons melted unsalted butter with 1 teaspoon Worcestershire sauce, 1 tablespoon poppy seeds, 1 tablespoon white sesame seeds, ½ tablespoon garlic powder, ½ tablespoon dried minced onion, ½ teaspoon kosher salt, and freshly cracked black pepper to taste. Brush this flavorful garlic butter sauce generously over the tops of all the buns. It’s the secret weapon that gives these sliders their signature, irresistible shine and nuttiness.

Step 7: Bake Until Golden and Melty

Loosely cover the sliders with foil and bake them in the preheated oven for 10 minutes. Then, remove the foil and bake for an additional 10 minutes until the tops turn golden brown, the cheese is melted and bubbly, and the whole kitchen smells like celebration. Keep a close eye to avoid over-browning—your perfect sliders are just about ready!

Step 8: Slice, Serve, and Dip!

Once out of the oven, slice between each roll carefully to separate the sliders. Serve them warm with little bowls of the hot au jus sauce on the side for dunking. There’s nothing quite like that tender roast beef, buttery bun, sweet onion, and garlicky broth combo. Grab one (or three) and enjoy every mouthwatering bite right away.

Top Tip

Making these Buttery Roast Beef Sliders with Caramelized Onions really shines when you keep a few key tricks in mind to get the best flavor and texture. Here are my favorite tips from cooking these sliders time and again.

Low and Slow Onion Cooking: Patience is everything—cooking your onions on medium-low for that full 45 minutes gives you jammy, deeply caramelized sweetness that transforms the sliders.
Use Hawaiian Rolls: Their soft, slightly sweet nature perfectly balances savory roast beef and rich garlic butter. I tried plain slider buns, but nothing beats Hawaiian for this recipe.
Brush Garlic Butter Both Before and After Baking: A double coating ensures that irresistible buttery crust on top while keeping the interior moist and flavorful.
Don’t Skip the Au Jus: It elevates these sliders from simple to spectacular. Dip each slider fresh and warm for maximum deliciousness.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

A tan baking tray holds five slices of light yellow bread with a soft texture. Each slice is spread with a layer of creamy white mayonnaise, which is smooth with small bits of green herbs mixed in. The slices are arranged close together, with three on the bottom and two on the top, placed on a white marbled surface. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

For a fresh, zesty touch, serve your sliders with a sprinkle of chopped fresh parsley or thyme on top. You could also offer pickled jalapeños or crisp dill pickle slices on the side for a tangy contrast. A small dab of additional garlic aioli or a smear of horseradish sauce can add an exciting kick too.

Side Dishes

These sliders are perfect alongside crispy shoestring fries, classic coleslaw, or a crunchy green salad with vinaigrette. Roasted vegetables or a warm bowl of creamy potato soup make cozy, hearty companions. For game day, consider pairing with chips and a zesty salsa or a tangy onion dip.

Make Ahead and Storage

Storing Leftovers

Once cooled, store any leftover sliders in an airtight container in the refrigerator. They'll stay fresh and tasty for up to 3 days, making them perfect for next-day lunches or snacks.

Freezing

While these sliders taste best fresh, you can freeze assembled sliders (without the garlic butter sauce brushed on top) by wrapping tightly in plastic wrap and placing them in a freezer bag. Freeze for up to 1 month. To enjoy, thaw overnight in the fridge before baking as directed.

Reheating

For perfectly reheated sliders that stay delicious and avoid sogginess, pop them into a preheated 375°F oven for about 10 minutes. This gently melts the cheese again and crisps the tops without drying out the roast beef.

Frequently Asked Questions:

Can I make this recipe without caramelized onions?

Absolutely! For a quicker 30-minute version, skip the caramelized onions altogether and jazz up store-bought mayonnaise with garlic, lemon, and mustard to mimic the aioli flavor. Your sliders will still be delicious and much faster to prepare.

Is it safe to eat the homemade garlic aioli with raw egg yolk?

If you're concerned about raw eggs, you can safely substitute mayonnaise for the aioli base. It still gives great creamy garlic flavor without the worry.

Which cheese works best for the sliders?

Melty cheeses like provolone, muenster, or Swiss are all fantastic choices. I like combining sliced cheese with shredded mozzarella to get that perfect gooey texture.

Can I prepare the sliders ahead of time?

Yes! You can assemble the sliders up to two days in advance without adding caramelized onions or garlic butter. Add those right before baking for best results.

Final Thoughts

These Buttery Roast Beef Sliders with Caramelized Onions Recipe have become a favorite in my kitchen for good reason—the perfect balance of savory roast beef, sweet onions, melty cheese, and rich, garlicky buttery buns is truly irresistible. Whether you're serving them for game day, a party, or a cozy night in, they never disappoint. I hope these tips and serving ideas help you enjoy every delicious bite!