French Onion Smash Burger Sliders (Print View)

Mini burgers packed with caramelized onions, melted cheese, and juicy beef, stacked on soft slider buns.

# Components:

→ Meats

01 - 1.1 lbs ground beef (80/20 blend)

→ Vegetables

02 - 3 large yellow onions, thinly sliced
03 - 2 tablespoons unsalted butter
04 - 1 tablespoon olive oil
05 - 1 teaspoon fresh thyme leaves (optional)

→ Breads & Dairy

06 - 8 slider buns
07 - 8 slices Gruyère or Swiss cheese

→ Condiments & Seasoning

08 - 1 tablespoon Worcestershire sauce
09 - 1 teaspoon kosher salt
10 - 1/2 teaspoon freshly ground black pepper
11 - 2 tablespoons mayonnaise (optional)
12 - 1 tablespoon Dijon mustard (optional)

# Directions:

01 - Heat unsalted butter and olive oil in a large skillet over medium heat. Add sliced yellow onions and a pinch of kosher salt. Cook, stirring occasionally, until onions are golden brown and deeply caramelized, about 25 to 30 minutes. Stir in Worcestershire sauce and thyme leaves (if using) in the final minutes. Set aside and keep warm.
02 - Divide ground beef into 8 equal portions (about 2 ounces each). Shape into balls and season each with kosher salt and freshly ground black pepper.
03 - Heat a cast iron skillet or griddle over medium-high heat. Place beef balls onto the hot surface and smash each firmly with a spatula to form thin patties. Sear for 2 minutes, then flip.
04 - Top each flipped patty with a generous portion of caramelized onions and a slice of Gruyère or Swiss cheese. Cover the skillet briefly to allow the cheese to melt, about 1 minute.
05 - Lightly toast the slider buns, cut side down, in a dry skillet or under a broiler until golden.
06 - Spread mayonnaise and/or Dijon mustard on the bottoms of the toasted buns if desired. Place each cheesy patty with caramelized onions on the bottom half of a bun, then top with the remaining buns. Serve immediately.

# Expert Advice:

01 -
  • Crowd-pleasing and addictive–you’ll catch people sneaking seconds before you finish the first round.
  • It’s the easiest way to get all the essence of French onion soup in a handheld package.
02 -
  • Once I rushed the onions on high heat and they turned bitter and crispy instead of sweet and jammy—patience is everything.
  • Covering the patties for just a minute is the secret to gooey, fully melted cheese without overcooking the beef.
03 -
  • Use an offset spatula or burger press for a perfectly thin smash—it makes a difference in the crust.
  • When toasting buns, watch closely and remove the moment they turn golden—seconds matter for perfect texture.
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