Bring salted water to a boil in a medium sauce pan. Prepare pasta according to package directions. Drain.

In the same pan, with the burner on medium heat, melt butter in the sauce pan until simmering. Sprinkle flour over the melted butter and whisk to form a pasta. Allow the pasta to cook until golden brown. Slowly whisk in milk until it creates a smooth sauce. Start with pouring in approximately 2/3 cup of milk. Use the remaining milk, up to 3/4 cup of milk for a thinner cheese sauce. Sprinkle in mustard powder. Add in shredded cheese and stir in until thick and creamy.

Add in drained pasta noodles and fold in to the cheese sauce until the noodles are all covered. Serve immediately.