Caramelized Onion & Swiss Cheeseburger

Serves 4 · 20 min prep · 35 min cook

Ingredients

• 1.5 lb ground beef (80/20)
• 1.5 tsp kosher salt
• 1 tsp black pepper
• 2 large yellow onions
• 3 tbsp butter
• 1 tbsp olive oil
• 2 thyme sprigs
• 4 Swiss cheese slices
• 4 brioche buns
• 2 tbsp Dijon mustard
• 2 tbsp mayonnaise
• 2 cups baby spinach

Instructions

1. 1Slice the onions thin. Melt butter with olive oil in a wide skillet over medium-low heat, add the onions and thyme, and cook slowly 25 to 30 minutes, stirring often, until deep golden, sweet, and jammy; season with salt and remove thyme stems.
2. 2While onions finish, form four beef patties, season both sides with salt and pepper, and press a center dimple.
3. 3Heat a second skillet or the same pan wiped clean over medium-high heat until hot.
4. 4Sear the patties 3 to 4 minutes per side for a good crust; in the final 90 seconds top each with a slice of Swiss cheese and a generous spoonful of the warm caramelized onions so the cheese melts under the onions.
5. 5Split and lightly butter the brioche buns, then toast cut-side down until golden and soft inside.
6. 6Stir Dijon and mayonnaise together and spread on the bottom buns.
7. 7Add a small handful of baby spinach for freshness, then set the onion-and-Swiss-topped patty on top.
8. 8Crown with the bun top, let rest 30 seconds so the cheese fully drapes, and serve while the onions are still glossy and hot.