Cook the elbow macaroni in a large pot of well-salted boiling water according to the package instructions.
In a saucepan, melt the butter over medium heat; stir in the flour until well combined and cook for 30 seconds, stirring constantly.
Add in the milk slowly, whisking constantly, until well combined. Cook and stir until bubbly.
Reduce the 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.