01 -
Heat the butter in a large skillet over medium heat. Add the thinly sliced onions and sprinkle with sugar. Cook the onions, stirring occasionally, until they turn a deep golden brown and become sweetly caramelized, about 20-25 minutes. If the onions start to stick, deglaze the pan with a splash of beef broth.
02 -
In a mixing bowl, season the ground beef with salt, pepper, and Worcestershire sauce. Mix well.
03 -
Shape the seasoned beef into 4 evenly sized patties. Cook the patties in a skillet or on a grill to your preferred level of doneness.
04 -
For garlic butter buns, mix minced garlic with softened butter and spread on the buns. Toast them until golden brown.
05 -
Place a cooked beef patty on the bottom half of each bun. Pile on a generous amount of caramelized onions and top with a slice of Gruyère or Swiss cheese.
06 -
Broil the assembled burgers briefly until the cheese is melted and bubbly.
07 -
Sprinkle fresh thyme over the melted cheese, cover with the top bun, and serve immediately.