1 lb ground beef
2 large yellow onions, thinly sliced
1 cup beef broth
1 tablespoon Worcestershire sauce
3 garlic cloves, minced
1 tablespoon all-purpose flour
1 teaspoon dried thyme
2 tablespoons butter
6 brioche buns
6 slices provolone or Swiss cheese
Salt and pepper to taste
Melt butter in a skillet and cook onions for 10 minutes until soft and golden.
Add beef, cook until browned, and drain excess fat.
Stir in garlic, thyme, salt, and pepper. Sprinkle flour over beef and mix.
Add broth and Worcestershire sauce. Simmer 5 minutes until slightly thickened.
Toast buns, spoon beef mixture onto each, and top with cheese.
Cover briefly to melt cheese, then serve hot.
For extra cheesiness, broil assembled sandwiches for 1–2 minutes.
Garnish with crispy fried onions for added crunch.