Make-Ahead Beef & Mushroom Pot Pies are a healthy, festive, and fun holiday meal reminiscent of the frozen pot pies of my 60s childhood, only healthier and tastier. You can make the filling ahead of time and even freeze it for a month. When ready to serve, thaw the filling, fill the baking dishes, and cover with frozen puff pastry before you bake. Your guests will be wowed!