For the Caramelized Onions:

• 3 large yellow onions, thinly sliced
• 2 tablespoons butter
• 1 tablespoon olive oil
• 1/2 teaspoon salt
• 1/2 teaspoon sugar (optional, for faster caramelization)
• 1/4 cup beef or chicken broth
• 1/4 teaspoon Worcestershire sauce

For the Burger Patties:

• 1 pound ground beef (80/20 for the best flavor)
• 1 teaspoon garlic powder
• 1 teaspoon onion powder
• 1/2 teaspoon smoked paprika
• 1/2 teaspoon dried thyme
• 1 teaspoon salt
• 1/2 teaspoon black pepper

For Assembly:

• 4 brioche buns
• 4 slices Gruyère or Swiss cheese
• 2 tablespoons mayonnaise (optional)
• 1 tablespoon Dijon mustard
• Fresh thyme sprigs (optional, for garnish)