To start, bring a dutch oven or big pot of salted water to a rapid boil. Once boiling, add your shell noodles and cook until they reach al dente – about 4 minutes. Once cooked, drain pasta and set aside.
Grate the cheese. It is important to use freshly grated cheese for making mac and cheese for it to be extra creamy. Avoid pre-shredded and bagged cheese, as they contain starch and preservatives that can make the sauce gritty.
In a heavy-bottomed saucepan, melt the butter over medium heat until melted. Add in the flour and continue to whisk, constantly cooking until the mixture turns a light brown.
Reduce heat to low and gradually add in the milk. The mixture will look lumpy and thick at first but continue whisking, and the mixture will thin out as you add the rest of the milk.
Increase the heat back to medium and cook the mixture for another 4-5 minutes or until the sauce thickens.
Reduce the heat to low and add ground mustard.
Add the grated cheese and stir until melted; however, do not let it boil, as this will cause the cheese to become gritty.
To finish, pour the cooked pasta noodles into the cheese sauce and combine until the noodles are evenly coated. Season with salt and pepper to taste.
This creamy white cheddar mac and cheese is best served hot.