Preheat oven to 400 degrees. Saute the onion in 1 tbs. oil, for about 3-5 minutes. Add the mushrooms and cook for another few minutes. Add the garlic, parsley, salt and pepper. Cook for about 2 minutes. Don't burn the garlic. Set aside and let cool.
Mix the pate until smooth. Set aside. Follow the puff pastry directions. The rolled out pastry has to be larger than the beef because you have to wrap it around the beef.
Brush the sides of the pastry with the egg wash, reserve the rest of the egg mixture. Place the pate mixture down the middle of the pastry and spread out. Place the beef on top of the pate and spread the mixture all over the beef. Roll up the pastry covering all the meat. Vent the pastry, in a few spots, using a sharp knife.