Prepare the pasta according to the directions on the box. Melt the butter over low heat in a medium sauce pan. Add in the flour to make a roux, whisking constantly. Cook about 1 minute before whisking in the milk. Continue whisking as the sauce thickens. Remove from the heat. Whisk in the seasonings (mustard, salt, hot sauce). Add in the cheeses using a spatula or wooden spoon until the sauce is smooth.
Mmmm! I saw this on The Pioneer Woman show on Food Network today and decided I'm going to make it for a cookout we are going to on Monday! Along with my yummy Cheesecake Bars! I'll be sure to take the calories out along the way! Ha!