Boil the pasta to al dente according to package directions. Drain over a colander and let cool slightly while you make the sauce.
1 pound dry medium shell pasta
Melt the butter in a large pot over medium heat. Whisk in the flour and cook until slightly golden and no longer floury-smelling.
6 tablespoons unsalted butter, ¼ cup all-purpose flour
Gradually pour in the milk first, then cream, while whisking continuously.
2 cups whole milk, 1 cup heavy cream
Once the mixture starts to bubble and thicken, stir in the salt, dried mustard, and pepper.
1¼ teaspoons kosher salt, ½ teaspoon dry mustard powder, freshly ground black pepper
Take the skillet off the heat. Then, add in the cheese and stir until completely melted and incorporated.
4 cups freshly shredded Vermont Cheddar cheese
Add the pasta to the skillet and stir to coat. Taste, and add more salt if needed.