Pour whole box of pasta into a large skillet (approximately 12 inches in diameter). Pour 3 cups of cold water into the pan, ensuring that the water covers the pasta. Turn the burner to high, then set your timer for 10 minutes (optional: add a bit of salt to taste).
Cook on high, stirring occasionally, until almost all of the liquid has evaporated.
Add dry mustard and cream and bring to a simmer then, remove the skillet from heat and gently fold in the sharp Cheddar, Parmigiano and parsley. Serve immediately.
