Into a food processor, pulse up the Button Mushroom (200 gram), Yellow Onion (1), and Garlic (2 clove). Set aside while you are working on the beef.
Chop down the Beef (500 gram) into small pieces. Season with Salt and Pepper (to taste), and fry them inside a pan with some Olive Oil (to taste).
Cut each Puff Pastry (3) into 6 pieces. On each piece, put your mushroom mixture, together with a piece from your fried beef. Wrap up each pastry, brush with the Egg (1), and bake inside a preheated oven 200 degrees C (400 degrees F) for about 20 minutes.