Creating French Dip Squares is straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
2. Prepare Pastry: Roll out the thawed puff pastry on a lightly floured surface. Cut each sheet into 4 squares, making a total of 8 squares.
3. Mix Ingredients: In a bowl, combine the beef broth, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Stir well to combine.
4. Layer Ingredients: On half of each pastry square, layer slices of roast beef, followed by a mix of provolone and mozzarella cheese.
5. Fold Pastry: Fold the other half of the pastry over the filling to create a pocket. Press the edges firmly to seal.
6. Brush with Egg Wash: Brush the top of each square with the beaten egg for a golden finish.
7. Bake: Place the squares on the prepared baking sheet and bake in the preheated oven for 25-30 minutes, or until golden brown and puffed.
8. Prepare Au Jus: While the squares are baking, heat the remaining beef broth in a small saucepan. Bring it to a simmer and keep warm.
9. Cool: Once baked, allow the squares to cool for 5-10 minutes before serving.
10. Serve: Slice the squares in half and serve with warm au jus for dipping.