In a large pot, bring water to boil with 1 tsp of salt.
Once you have a rolling boil, add the pasta.
Cook the pasta until al dente. In my experience, this is usually 1 to 2 minutes before the package instructions. I err on the side of undercooked because once you add the pasta to the cheese sauce, you will continue the cooking process.
Drain the pasta, reserve about a cup of the cooking liquid, and set aside.
In a separate saucepan, add the butter and cook until melted and foaming, but not browning.
Whisk in the flour to make a rue.
Add the milk, sour cream, and garlic powder, and continue to whisk until smooth.
Add the cheese blend and stir with a wooden spoon until smooth.
Taste the cheese sauce and adjust the seasoning as needed.
Add the cooked pasta to the cheese sauce and stir.
Add pasta water, only if necessary, and stir until you get the desired consistency.
Serve with a healthy dash of coarse black pepper and parsley.
