Keto French Dip Sliders

Ingredients

• 5 tablespoons unsalted butter, divided
• 1 medium yellow onion, thinly sliced
• 2 thyme sprigs, plus 1/2 teaspoon chopped thyme
• salt & pepper for seasoning
• 1 package (12-count) low-carb slider rolls
• 1 pound thinly sliced deli roast beef
• 6 slices provolone cheese
• 1 teaspoon chopped fresh parsley, plus more for serving
• 1/4 teaspoon garlic powder
• 1 large garlic clove, minced
• 1 ½ cups beef broth
• 1 tablespoon Worcestershire sauce