French Onion Burger Recipe

Heat a large skillet over medium-low heat. Add butter and olive oil so the butter doesn't burn.

Add the thinly sliced onions and sprinkle with 1/2 tsp kosher salt. Cook, stirring every few minutes, until the onions are soft and beginning to brown—about 20–30 minutes. Reduce heat if they begin to darken too quickly.

If you want to speed the process and deepen color, sprinkle 1/4 tsp sugar after 10 minutes and continue to cook. Stir frequently for even caramelization.

Toward the end, increase heat to medium and add 1 tablespoon red wine or balsamic vinegar to deglaze the pan, scraping any browned bits. Cook another 1–2 minutes until the liquid is mostly evaporated. Remove from heat and keep warm.

Divide the ground beef into 4 equal portions (for 4 thin patties) or 2 portions (for larger patties). Lightly form into patties about 3/4 inch thick—do not overwork the meat.

Season both sides of each patty with kosher salt (about 1/4 tsp per side) and freshly ground black pepper. Brush or rub 1 tsp neutral oil on the cooking surface (griddle or skillet) and heat to medium-high.

Cook patties 3–4 minutes per side for medium (adjust timing for doneness). During the last minute of cooking, add Swiss cheese slices on top of each patty and cover the pan to melt the cheese (about 1 minute). Remove patties and tent with foil to rest briefly.

If using a grill, oil the grates and cook similarly; add cheese and close the lid to melt.

While the patties cook, stir 1 tablespoon Worcestershire sauce into the reserved pan juices or into a small bowl to brush onto buns or finish patties if desired.

In the skillet used for the patties (leave any browned bits), pour in 1 cup beef broth and 2 tablespoons red wine (or extra broth). Bring to a simmer over medium heat, scraping up browned bits from the pan.

Stir in 1 teaspoon Worcestershire sauce and 1/2 teaspoon soy sauce (if using). Taste and season with 1/4 tsp freshly ground black pepper; add salt only if needed because the broth may already be salted.

To slightly thicken, mix 1/2 tsp cornstarch with 1 tsp cold water to make a slurry. Whisk the slurry into the simmering jus and cook 1 minute until glossy and slightly thickened. Keep warm.

Split the buns and lightly butter the cut sides. Toast buttered sides on a hot skillet or griddle until golden, about 1–2 minutes.

Place one cheese-topped patty on the bottom bun, mound a generous portion of caramelized onions over the cheese, and top with the bun crown.

Serve each burger with a small ramekin or shallow bowl of warm au jus for dipping, or spoon a few tablespoons of jus over the burger just before serving for extra flavor.