Prepare pasta according to package directions.
In a medium saucepan, melt butter over low heat. Add flour to make a roux, whisking constantly. Cook about 1 minute before whisking in the milk. Continue whisking as the sauce thickens. Remove from heat.
Whisk in mustard, salt and hot sauce. Add cheeses using a spatula or wooden spoon until the sauce is smooth.
Fold in pasta until it’s heated through. Serve immediately.