Bring a large pot of well-salted water to a boil. Add the macaroni and cook 1 minute shy of al dente according to package directions.
Reserve 1/2 cup pasta water, then drain. Do not rinse; the starch helps the sauce cling.
In a large pot or deep skillet, melt the butter over medium heat. Sprinkle in the flour and whisk for 1 minute to cook off the raw taste. Keep it blond, not brown.
Slowly whisk in the milk, then the half-and-half. Bring to a gentle simmer; the sauce will lightly thicken and coat the back of a spoon.
Season with mustard powder, garlic powder, onion powder, a few dashes of hot sauce, and a pinch of salt and pepper.
Reduce heat to low. Add the cubed Velveeta and whisk until completely melted and smooth.
Stir in the shredded sharp cheddar until just melted. If the sauce seems too thick, loosen with a splash of milk or reserved pasta water.
Add the cooked macaroni to the sauce and stir gently until every noodle is coated and glossy.
Taste and adjust seasoning with salt and pepper. Serve hot, right away, with a crack of black pepper on top.
