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 onion and cook 3–4 minutes until tender. Stir in minced garlic, half the black pepper, and a pinch of salt; cook for 1 additional minute. Remove from heat and set aside.
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 starting from the wide end toward the point. Place roll ups seam-side down on the prepared baking sheet, spacing them evenly.
05 - Melt remaining butter and brush over the tops of each roll up. Sprinkle with remaining black pepper and dried thyme if desired.
06 - Bake at 375°F for 12–15 minutes until the tops are golden brown and the cheese is melted.
07 - While roll ups bake, combine beef broth and Worcestershire sauce in a small saucepan. Heat over low setting and simmer for 5 minutes to develop flavor.
08 - Serve roll ups hot alongside warm au jus sauce for dipping.