Combine the cheese sauce and macaroni in a large mixing bowl and mix well. Lightly grease a 6 1/2 by 10-inch casserole dish with the remaining 1/2 teaspoon butter.
Continue stirring until the cheese melts. Remove the white sauce from the heat and stir in the cheese. Add the remaining 1/2 teaspoon salt and the white pepper and continue whisking until the sauce is smooth and thick enough to coat the back of a wooden spoon, about 8 minutes. Slowly add the milk, whisking constantly. Add the flour and cook, stirring constantly, for 2 minutes. In a small, heavy saucepan, melt 2 tablespoons of the butter over medium heat. Set on low for 1.5 hours with the lid on, stirring occasionally. Add all but 1 1/2 cups of cheese and stir until melted. Add 2 cups (8 ounces) uncooked macaroni, 2 cups milk, 1/2 lb cubed Velveeta cheese, 1/2 cup shredded cheddar, 2 tbsp butter, 1/2 tsp each of garlic powder, onion powder, and dry mustard powder to the Crock Pot and stir well. When cooking your pasta, be sure to cook it just until al dent. Remove the foil and return the mac and cheese to the oven to continue baking for 10-15 minutes, or until the top is bubbling and golden brown.
Pour egg mixture back into the sauce, stirring constantly until completely incorporated. Place mac and cheese in the oven and bake for 15 minutes. Add the macaroni and cook, stirring occasionally, until tender, about 8 minutes. Slowly drizzle in 1/4 cup of the sauce it into beaten egg while whisking egg mixture. Put the water, 1/2 teaspoon of the salt, and the oil in a large, heavy saucepan over high heat and bring to a boil.