Return the pasta to the pot with the reserved pasta water. Add the butter and milk and cook over medium heat until the butter is melted and the mixture is simmering. Slowly add the cheese, ½ cup at a time, stirring constantly until melted before adding the next ½ cup. Once all the cheese is melted, add the Pimento peppers and kosher salt. Stir to combine and season to taste.
Serve with fresh apple slices (keep them in a Ziploc® brand snack bag for freshness).