1 puff pastry
1 trussed beef (a tender piece best; i.e. filet mignon)
200 gr (7 ounces) of mushrooms
2 tablespoons of olive oil
1 teaspoon of milk
Salt and pepper
Rinse the mushrooms and cut them. Cut the onions.
Mix the onions and mushroom until it looks like a sauce. While it's mixing, put the beef in a friying pan with one spoon of olive oil and make sure it is browned on both sides. Put it to the side and wait for it to be cool.
Take your mushroom mixture and put it in a friying pan with the second spoon of olive oil.
Cook it for 15 minutes at medium temperature. Put it away.
Separate the egg whites from the yolk.
Unroll your puff pastry on the oven rack. Using a brush, moisten around the pastry with the egg whites.
Put 3/4 of the sauce in the middle of the pastry.
Put the beef on the top of it. Cover the beef with the rest of the sauce.
Cover the beef with the puff pastry, making sure it is well closed.
Using a brush, cover the pastry with the egg yolk plus milk.Cook it in the oven at 400 degres during 35 / 40 minutes depending on how you like the meat cooked. A potato puree or French fries make excellent accompaniments.