Slow-Caramelized Onion Swiss Smash Cheeseburger

Smash burgers trace their crisp edges to American diner griddles, where loose beef hits hot metal and seals in flavor. Slow-caramelized onions turn jammy and sweet beside melted Swiss on a soft brioche bun for a rich, savory bite.

Serves 4 · 10 min prep · 35 min cook

Estimate for one serving

• 680 cal
• 36g protein
• 34g carbs
• 44g fat
• 3g fiber

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Ingredients

• 1.5 lb ground beef (80/20)
• 2 large yellow onions
• 3 tbsp unsalted butter
• 1 tbsp olive oil
• 1.5 tsp kosher salt
• 3/4 tsp black pepper
• 1 tsp fresh thyme leaves
• 4 Swiss cheese slices
• 4 brioche burger buns
• 3 tbsp mayonnaise
• 1 tbsp whole-grain mustard
• 2 cups baby arugula
• 1/2 tsp garlic powder

Instructions

1. 1Peel and slice the onions into thin half-moons. Melt the butter with the olive oil in a wide skillet over medium-low heat, then add the onions and salt.
2. 2Cook the onions slowly, stirring every few minutes, for 25 to 30 minutes until they turn deep golden brown and jammy. Stir in the thyme during the last 5 minutes and keep them warm.
3. 3While the onions caramelize, divide the ground beef into four loose balls. Do not overwork the meat so the smash stays tender.
4. 4Heat a large cast-iron skillet or flat-top griddle over high heat until smoking hot. Place each beef ball on the surface and immediately smash it thin with a sturdy spatula or burger press. Season the tops with salt, pepper, and a dusting of garlic powder.
5. 5Cook the smashed patties 2 to 3 minutes until the edges are lacy and deeply browned. Flip once, then top each with a Swiss cheese slice.
6. 6Cover the skillet briefly or tent with foil for 45 to 60 seconds so the Swiss melts into a glossy blanket over the crusty beef.
7. 7Split and lightly toast the brioche buns cut-side down in the same pan or a toaster until just golden and warm.
8. 8Stir mayonnaise and whole-grain mustard together and spread on both bun halves.
9. 9Place arugula on each bottom bun, set the cheesy smash patty on top, then pile on a generous spoonful of the warm caramelized onions. Cap with the top bun.
10. 10Serve right away so the Swiss stays stretchy and the sweet onions contrast the peppery arugula and crisp smash edges.