Step 1

Bring 2 quarts of water to boil in large soup kettle. Add salt and pasta. Using package directions as a guide, cook until al dente. Drain. To prevent sticking, drain and immediately pour onto a large lipped baking sheet and let cool while preparing sauce.

Step 2

Meanwhile, microwave the milk and chicken broth in a 4-cup Pyrex measuring cup or bowl until hot and steamy (not boiling). Melt butter in the empty pasta pot; whisk in flour, then hot milk mixture. Continue to whisk until thick and bubbly, 3 to 4 minutes. Whisk in mustard, Parmesan and pepper. Turn off heat, stir in cheddar until melted.

Step 3

Add drained pasta (and optional flavoring ingredients, see notes) to sauce, and stir until everything is well combined over low heat. Stir to heat through, and thin with a little water if the sauce is too thick. Serve hot.