Melt butter and olive oil in a skillet over medium-low heat. Add the sliced yellow onions and cook slowly for 25-30 minutes, stirring occasionally, until they turn a rich, dark brown. Let cool slightly.

Spread a thin, even layer of softened cream cheese over each of the 4 soft white flour tortillas to act as a binder.

Lay 2-3 slices of provolone cheese down the center of each tortilla. Arrange folds of the thinly sliced roast beef over the cheese, and top evenly with the caramelized onions.

Tightly roll each tortilla into a cylinder. Wrap in plastic wrap and chill in the refrigerator for 20 minutes to firm up the cream cheese for easy slicing.

Preheat oven to 300°F (150°C). Unwrap the tortillas and use a serrated knife to cut into thick, 1-inch (2.5cm) pinwheels. Place them flat on a baking sheet and bake for 5-7 minutes until the provolone is glossy and melted.

While the pinwheels warm, whisk the beef broth, Worcestershire sauce, and soy sauce in a small saucepan. Simmer for 5 minutes. Pour into a small white dipping bowl and garnish with finely chopped fresh green parsley flakes.