Certainly, live crayfish will make the best meal. However, if you can only find frozen crayfish make sure you thaw them in the refrigerator (it takes a bit longer, but will keep the crayfish juicier).
Porcini may be hard to find. But if you can not get hold of them in the gourmet markets you can use white mushrooms and dried porcini (they are readily available).
Serve with mayonnaise, mixed with finely chopped chervil, and sautéed mushrooms.