In a large pot combine the elbow macaroni, water, and salt. Bring the mixture to a boil over high heat, stirring occasionally.
Reduce the heat to medium and simmer the pasta, stirring frequently, until the water is almost completely absorbed and the pasta is al dente, about 8-10 minutes.
Stir in the whole milk, butter, flour, garlic powder, and ground mustard. Continue to cook, stirring constantly, until the mixture thickens and coats the back of a spoon, about 2-3 minutes.
Remove the pot from the heat and gradually stir in the shredded white cheddar cheese and grated Parmesan cheese until melted and smooth. Then it's ready to serve and enjoy!
