01 -
2 large onions, sliced.
02 -
2 tablespoons butter.
03 -
1 tablespoon olive oil.
04 -
1 teaspoon sugar.
05 -
1/4 teaspoon salt.
06 -
1/4 cup beef broth.
07 -
1/4 cup white wine (optional).
08 -
1 1/2 pounds ground beef (80/20).
09 -
1 teaspoon Worcestershire sauce.
10 -
1 teaspoon salt.
11 -
1/2 teaspoon black pepper.
12 -
4 slices Gruyère cheese.
13 -
4 brioche buns.
14 -
2 tablespoons butter, melted.
15 -
Fresh thyme (optional).