2 pounds starchy potatoes, peeled and sliced 1-inch thick
1/2-2/3 cup milk or half-and-half
1 1/2 cups shredded Gruyère cheese
1 rounded tablespoon Dijon mustard
Salt and pepper
Boil the potatoes until tender, about 15 minutes. Drain the potatoes and return them to the hot pot. Mash with the milk or half-and-half. Stir in the cheese and mustard to combine; season with salt and pepper.