President Reagan's Favorite Macaroni and Cheese

Well, it may be from my kitchen, and it may have come out of my school's cookbook, but the recipe is known as:

President Reagan's Favorite Macaroni and Cheese
1/2 lb. macaroni
1 t. butter
1 egg, beaten
1 t salt
1 t dry mustard
3 c grated cheese, sharp
1 c milk

Boil macaroni in water until tender and drain thouroughly.  Stir in butter and egg.  Mix mustard and salt with 1 T hot water and add to milk.  Add cheese leaving enough to sprinkle on top.  Pour into buttered casserole, add milk, sprinkle with cheese.  Bake at 350 degrees for about 45 minutes or until custard is set and top is crusty.