Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan cheese, chopped parsley, egg, minced garlic, onion powder, Italian seasoning, and salt and pepper. Mix until well incorporated.

Form the meat mixture into small meatballs, roughly 1 inch in diameter, yielding about 12 meatballs.

On a lightly floured surface, roll out the thawed puff pastry sheets and cut each sheet into squares, approximately 4 inches on each side.

Place one meatball in the center of each puff pastry square and fold the corners over the meatball, pinching the seams together tightly.

Coat the tops of the assembled pastries with the beaten egg for a golden finish.

Arrange the pastries on the lined baking sheet and bake for about 20 minutes or until golden brown.

Allow the pastries to cool slightly on a wire rack before serving warm, optionally with marinara sauce for dipping.