Melt the butter in a saucepan and whisk in the flour. Add the onions and cook over low heat until they are tender. Add veal stock, red wine, roasted garlic, garlic powder, salt and pepper. Turn up the heat and whisk until you reach a slow boil and all the lumps are gone. Add the mushrooms, reduce the heat, and simmer for 10 minutes. Heat a skillet, and then add the olive oil. Add the beef and cook until medium rare. Transfer the beef to a baking dish and cover with the mushroom gravy. Cover with the puff pastry sheets and bake until the pastry is golden brown.