The Preparation
Cook pasta in well-salted boiling water until al dente. Drain, reserving 1/2 cup pasta water.
Melt butter in a large saucepan over medium heat. Whisk in flour and cook for 2 minutes.
Gradually whisk in warm milk, then cream. Cook, stirring constantly, until thickened, about 5 minutes.
Remove from heat and stir in mustard, garlic powder, and cayenne.
Add cheeses a handful at a time, stirring until melted and smooth.
Season with salt and white pepper.
Toss pasta with sauce, adding reserved pasta water if needed to loosen.
Serve immediately.
