Fantastic. I've made it five Thanksgivings in a row, sometimes using the different cheeses called for, and sometimes using almost all smoked gouda. Sometimes it's been grainy, so one year I figured out the following adjustments and it was perfect! ANTI-GRAININESS VARIATION:
INGREDIENTS: 8 T (1 stick) butter, 6 T flour, 4 c milk + 2 c heavy cream, a small amount of processed cheese for stabilizing (i.e. 2 slices American), 4-6 c shredded cheese (I used 2 half-lb packages of smoked gouda, 1 c grated parmesean, 1 c shredded cheddar), 1/2 t paprika, pasta. TOPPING: 1 c panko crumbs, 1/2 c parm, 1/2 t cayenne pepper, optional t of parsley for color, 2-3 T melted butter (or olive oil). STEPS: Melt butter. Wisk in flour to make roux. Let bubble, but don't burn. Add a little milk/cream and stir until roux is incorporated. Add the rest of the milk/cream. Heat over medium-high heat, wisking constantly, until thickened. Lower heat and simmer, stirring occasionally, 10 mins. REMOVE FROM HEAT BEFORE ADDING CHEESE. Add a small amount of a processed cheese, which stabilizes the sauce/prevents graininess. Stir until melted. Add shredded cheese, cover, and let sit until melted, stirring occasionally. Turn on low heat if necessary to get it to melt, but don't overheat-DON'T let it boil. Add paprika. Cool. Make pasta and cool. Add cooled pasta to cooled cheese sauce and pour into 13x9 pan. Refrigerate until chilled. Combine topping ingredients and sprinkle over pasta. Bake at 400 until golden.