Bring 6 cups of water to a boil; add 1 tablespoon of salt. Add macaroni noodles and cook to al dente. Drain in strainer and run cold water over noodles for a few minutes to bring the temperature down.
Preheat oven to 375°F. Grease a 3-quart casserole dish with butter. Combine evaporated milk, sugar, eggs and sour cream in a mixing bowl and whisk thoroughly. Add macaroni to casserole dish. Stir in evaporated milk, egg and cream mixture. Mix thoroughly. Add butter, margarine, pepper, Velveeta cubes, sharp cheddar and Colby Jack cheeses. Mix well while adding whole milk. Pack down mixture into casserole dish and top with fancy mild cheese.