I got this recipe from a Myra Waldo around the world cookbook many, many years ago and it is still my favorite Tetrazzini recipe. I use the sauce in many other recipes ( chicken divan, etc.) and as a substitute for cream of.... in some recipes. It makes a lot. (She suggested putting it in two 2 1/2 quart casseroles and freezing one.) It is also good made with leftover turkey. I often increase the amounts of the cheeses.