Smash Burgers with Caramelised Onion and Gruyère

Ingredients

• 700 g beef mince (80/20 fat ratio)
• 1 tsp kosher salt
• ½ tsp black pepper
• 2 large onions, thinly sliced
• 2 tbsp unsalted butter
• 1 tsp balsamic vinegar
• 8 slices Gruyère cheese
• 4 brioche burger buns
• 3 tbsp mayonnaise
• 1 tbsp Dijon mustard
• 1 tsp Worcestershire sauce
• 4 leaves iceberg lettuce
• 2 tomatoes, sliced

Instructions

1. 1

   Melt butter in a heavy skillet over medium-low heat. Add sliced onions and a pinch of salt. Cook, stirring every 5 minutes, for 30–35 minutes until deep golden and jammy. Stir in balsamic vinegar, cook 1 more minute, and set aside.

2. 2

   Divide the beef mince into 8 equal balls (about 85 g each). Do not overwork the meat — loosely packed is key to a good crust.

3. 3

   Heat a cast-iron pan or flat griddle over high heat until it begins to smoke. Lightly oil the surface.

4. 4

   Place two beef balls in the pan, immediately press firmly with a flat spatula or smash tool to roughly 1 cm thick. Season the top with salt and pepper.

5. 5

   Cook for 2 minutes until edges are crispy and brown, then flip. Immediately top each patty with a slice of Gruyère, add a splash of water to the pan and cover briefly to melt the cheese. Cook 1 more minute.

6. 6

   Mix mayonnaise, Dijon, and Worcestershire for the sauce. Toast the buns cut-side down in butter.

7. 7

   Build each burger: sauce on both bun halves, lettuce, tomato, a double patty stack, and a generous spoonful of caramelised onions. Serve immediately.