01 - Preheat oven to 375°F. Line baking sheet with parchment paper.
02 - Heat 1 tbsp butter in small pan over medium heat. Add onion and sauté 3-4 minutes until tender. Add garlic, half the black pepper, and pinch of salt; cook 1 minute longer. Set aside.
03 - Unroll crescent dough and separate into 8 triangles. Place roast beef slices and sautéed onion mixture onto wide end of each triangle. Sprinkle cheese evenly over filling.
04 - Roll each triangle tightly from wide end to point. Place seam-side down on prepared baking sheet.
05 - Melt remaining butter and brush over tops of roll ups. Sprinkle with remaining black pepper and thyme.
06 - Bake for 12-15 minutes until golden brown and cheese is melted.
07 - Combine beef broth and Worcestershire sauce in small saucepan. Heat over low heat, simmering for 5 minutes to create dipping sauce.
08 - Serve hot roll ups immediately with warm au jus for dipping.