01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a skillet over medium heat, melt butter with olive oil. Add sliced onions and cook, stirring occasionally, until golden and caramelized, about 8-10 minutes. Season with salt, pepper, garlic powder, and thyme.
03 - Lay tortillas flat. On each, layer sliced roast beef, caramelized onions, and one slice of provolone cheese.
04 - Tightly roll up each tortilla and place seam-side down on the prepared baking sheet. Optionally, brush the tops lightly with olive oil for extra crispness.
05 - Bake for 10-12 minutes, or until tortillas are golden and crisp, and cheese is melted.
06 - Meanwhile, combine beef broth, Worcestershire sauce, soy sauce, onion powder, and garlic powder in a small saucepan. Bring to a simmer over medium heat and cook for 5-7 minutes. Adjust seasoning if necessary.
07 - Remove roll ups from the oven, let cool slightly, then slice in half if desired. Serve warm with hot au jus for dipping.