01 - Preheat oven to 375°F. Line a baking sheet with parchment paper and set aside.
02 - Heat 1 tbsp butter in a small skillet over medium heat. Add sliced onion and sauté for 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 from the wide end toward the tip. Place seam-side down on the prepared baking sheet. Melt remaining butter and brush over the tops. Sprinkle with remaining black pepper and dried thyme if desired.
05 - Bake at 375°F for 12–15 minutes until the pastry is golden brown and cooked through.
06 - While roll ups bake, combine beef broth and Worcestershire sauce in a small saucepan. Warm over low heat, allowing it to simmer gently for 5 minutes to develop flavor.
07 - Transfer hot roll ups to a serving platter. Serve immediately with warm au jus for dipping.