Season the beef with salt and pepper and set a cube on each pastry square. Fold the pastry over the beef, neatly tucking in the corners. Arrange the pastries seam side down on a large baking sheet lined with parchment paper. The recipe can be prepared to this point and frozen for up to 1 week.
Lightly brush each pastry with the beaten egg. Bake for 1. 0 to 1. Let cool slightly, then transfer to a platter and serve.