Cook the elbow macaroni in a large pot of salted water, per package instructions.
In a large saucepan, melt the butter over medium heat; stir in the flour until well combined and cook for 30 seconds, stirring constantly. Very slowly add in the milk, whisking constantly, until well combined; cook and stir until bubbly.
Reduce heat to low and add the cheddar cheese, American cheese, and grated Parmesan cheese; stir until melted. Season with sea salt and freshly cracked pepper, to taste.
Add the cooked & drained noodles to the sauce. Toss to coat evenly then turn the stove off and let it sit for 3-5 minutes to allow the sauce to thicken. Stir, taste & re-season, if needed.
Serve with extra shredded cheddar or Parmesan cheese for sprinkling on top. Enjoy.