As the water starts coming to a boil, add 1/2 cup whole milk to the cooking water. Cook the macaroni 2 minutes less than the time stated on the box. Drain the pasta in a colander and reserve 1 cup of the cooking liquid.
While the noodles cook, heat 4 tbs butter, 0.5 oz American Cheese, and 1/4 cup whole milk in a separate saucepan over medium-low heat, stirring frequently, until the cheese melts.
Return the drained noodles to the cooking saucepan. Add the seasoning packet from the box, 1/2 tsp garlic powder, 1/4 tsp paprika, 1 pinch ground cayenne pepper, and the melted cheese mixture; mix gently until completely combined. Season with salt and pepper to taste. If the mac and cheese is not as wet as you prefer, drizzle reserved cooking liquid into the pan a little at a time—do not add more than 2 Tbs at a time—until you reach the desired sauciness. Top with grated parmesan cheese.