Caramelize the Onions: In a skillet over medium heat, add butter and thinly sliced onions. Cook, stirring occasionally, until the onions are golden and caramelized, about 20 minutes. Set aside to cool.
Assemble the Pinwheels: Preheat your oven to 400°F. Roll out the puff pastry sheet on a lightly floured surface. Arrange the onions over the pastry. Layer on the provolone cheese and roast beef slices.
Roll and Slice: Carefully roll up the pastry, starting from one edge and rolling tightly. Use a sharp knife to slice the roll into 1-inch rounds. Place them on a baking sheet lined with parchment paper.
Bake: Brush each pinwheel with the beaten egg wash. Bake for 20 minutes or until golden and puffed.
While the pinwheels bake, combine the beef stock, Worcestershire sauce, garlic powder, and onion powder in a small saucepan. Bring to a simmer and cook for a few minutes until warm.
Arrange the pinwheels on a platter, garnish with diced rosemary and serve with the au jus dipping sauce in a small bowl. Cheers!