Preheat oven to 350° and grease a 9"-x-13" baking pan with cooking spray. In a large skillet over medium-high heat, melt butter. Add onion and thyme sprigs and cook, stirring occasionally, until onions begin to soften and turn golden, about 5 minutes. Season with salt and pepper and reduce heat to medium. Continue cooking, stirring occasionally, until onions are soft and caramelized, 10 to 15 minutes more. Let cool to room temperature.

Assemble pinwheels: On a lightly floured surface, unroll crescent dough and separate into two rectangles (per can - so four rectangles total). Pinch together seams. Top each rectangle with provolone, roast beef, and caramelized onions.

Starting with the short side, roll up each rectangle. Pinch edges to seal then cut each roll into about 1" slices. Place cut side up in the baking dish. Sprinkle with thyme leaves.

Bake until dough is golden, 35 minutes.

Meanwhile, make au jus: In a small saucepan over medium heat, melt butter. Stir in garlic and cook until fragrant, about 1 minute. Add broth, Worcestershire, and thyme leaves and season with salt and pepper. Simmer until slightly reduced, 10 minutes.

Serve pinwheels warm with au jus for dipping.