1 lb ground beef

2 large onions, thinly sliced

2 tablespoons butter

1 teaspoon sugar

1/2 cup beef broth

2 tablespoons Worcestershire sauce

1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried thyme)

Salt and pepper to taste

4 slices of Gruyère or Swiss cheese

4 hamburger buns

1 clove garlic, minced (optional for garlic butter buns)

Additional butter for buns

Caramelize the Onions: Melt butter in a large skillet over medium heat. Add sliced onions and sugar. Cook for 20-25 minutes, stirring occasionally until deeply caramelized. Add beef broth to deglaze if needed.
Prepare the Burger Patties: While the onions cook, season the ground beef with salt, pepper, and Worcestershire sauce. Form into 4 equal-sized patties.
Cook the Burger Patties: Grill or cook patties in a skillet for 4-5 minutes per side until medium doneness.
Toast the Buns: For garlic butter buns, mix melted butter with minced garlic. Spread onto buns and toast until golden brown.
Assemble the Burgers: Place cooked patties on bun bottoms, top with caramelized onions and a slice of Gruyère or Swiss cheese.
Broil the Burgers: Place burgers under a broiler for a few minutes until cheese is melted and bubbly.
Serve: Garnish with fresh thyme and serve immediately.

Vegetarian Version: Replace beef patties with veggie patties or portobello mushrooms.

Cheese Variations: Swap Gruyère or Swiss with cheddar, mozzarella, or provolone for a twist.

Toppings: Add crispy bacon, sautéed mushrooms, or a fried egg for extra flavor and texture.

Gluten-Free: Use gluten-free buns or lettuce wraps for a gluten-free option.