Matty's Mac n Cheese

This is the recipe my brother in law Matt uses. (At the time he introduced us to this recipe, one of their friends persistently called him Matty much to his dismay. It may have been catching.) This recipe is so good it needs publishing and to be preserved online in case of tragedy.
Please note: Substitutions cannot be made. I have tried, it does not work. This recipe can, however, be trippled.
1 3/4 cups small elbow macaroni
1 1/4 cups EXTRA sharp cheddar and White Cheddar (about 5 oz) cut into 1/2 inch cubes
2 Tablespoons plus 2 teaspoons flour
1 1/2 teaspoons salt
1 1/2 teaspoons dry mustard powder
1/4 teaspoon ground white pepper (black pepper makes suspicious black flakes)
1/8 teaspoon cayenne pepper
1/8 teaspoon ground nutmeg
1 1/3 cups half and half
1 1/3 cups whipping cream
2/3 cup sour cream
2 large eggs
1 Tablespoon Worcestershire sauce
1 1/4 cups packed grated extra sharp cheddar
Preheat oven to 350* F. Lightly butter 9x13 glass baking dish. Cook macaroni al dente, drain, put into baking dish, and add cubed cheese. Combine dry ingredients. Add wet ingredients gradually while whisking. Pour over macaroni noodles and cubed cheese. Sprinkle grated cheese on top.
Bake for 25 minutes. Let stand for 10 minutes. (Resist the urge to sneak even just a bite. The sauce needs to thicken as it cools. If you take an early bite there is sauce that cannot claim noodles. (The voice of experience.)
Because we're lactose intolerant (and bad ones at that) I portion this delicacy into 1/2 cup Tupperware and freeze it for those snack time cravings...when I haven't had too much dairy that day.