Step 1

Boil pasta in a medium pot of boiling salted water until al dente, about 2 minutes less than per package instructions. Drain, reserving 1 cup pasta water.

Step 2

Return empty pot to medium heat and add butter. When butter melts and foams, add flour and whisk until darkened slightly, 1 to 2 minutes. Add mustard powder and whisk to combine. Slowly whisk in milk and vermouth. Bring to a boil, then reduce heat to medium and cook, stirring often, until thick enough to coat the back of a spoon, 3 to 4 minutes.

Step 3

Reduce heat to low and add cheese in 3 batches, starting with Raclette. Follow with Gruyere and Emmentaler. Whisk to fully combine after adding each cheese. Season with salt and pepper. Add pasta, stir to coat, and serve, sprinkled with parsley and more pepper.