01 - Preheat oven to 375°F. Line a baking sheet with parchment paper and set aside.
02 - Melt 1 tbsp butter in a small skillet over medium heat. Add sliced onions and cook for 3 to 4 minutes until tender. Stir in minced garlic, half the black pepper, and a pinch of salt. Cook for 1 additional minute, then remove from heat.
03 - Unroll crescent dough and separate into 8 triangles. Layer roast beef slices and the sautéed onion mixture onto the wide end of each triangle. Distribute shredded cheese evenly over the filling.
04 - Roll each triangle tightly from the wide end toward the point. Place seam-side down on the prepared baking sheet. Brush tops with remaining melted butter and sprinkle with remaining black pepper and thyme if desired.
05 - Bake at 375°F for 12 to 15 minutes until the tops are golden brown and the cheese is melted.
06 - While roll ups bake, combine beef broth and Worcestershire sauce in a small saucepan over low heat. Simmer gently for 5 minutes to develop flavor.
07 - Remove roll ups from oven and serve immediately with warm au jus sauce for dipping.