In a large pot filled with salty water, boil the macaroni for one minute less than the package directions.
Drain the pasta in a large colander, then toss with the additional 1 tablespoon of butter to coat the noodles and prevent sticking.
Preheat the oven to 325 degrees F and lightly mist a 9x13 casserole dish with non-stick spray. Shred the cheeses, by hand with a box grater, or in a food processor. Melt the remaining 1/2 cup of butter in a large pot over low heat, and stir in the flour until a smooth paste forms.
Slowly pour in 1 cup of the milk, while whisking.
When no lumps remain, add the rest of the milk and the cream.
Turn the heat up to medium and allow the sauce to thicken slightly (it should coat the back of a spoon).
Whisk in the salt, garlic powder, dry mustard, paprika, and pepper.
Whisk in about 1/3 of the shredded cheese, a handful at a time, allowing each addition to fully melt in before adding the next.
Pour the cheese sauce over the cooked macaroni, and stir until combined.
Transfer half the mixture to the prepared baking dish, then top with another 1/3 of the shredded cheese.
Layer the remaining mac and cheese on top, then sprinkle on the last 1/3 of cheese and bake until the cheese is melted (about 15 minutes).
Optional: Broil the top of the baked macaroni and cheese until bubbly and browned (3 to 5 minutes).