Preheat the oven to 375 degrees F.
Bring a large pot of salted water to a boil. Add the macaroni, cook for 8 - 9 minutes. Strain and set aside.
In a heavy-bottomed large pot over medium heat, melt the butter.
Sprinkle the flour, white pepper, salt, and cayenne pepper over the melted butter, whisking until smooth and the mixture has thickened slightly.
Stir in the milk ½ cup at a time ( feel free to eyeball it ), only adding the next half cup once the previous one has been incorporated entirely.
Add all of the medium cheddar cheese and half of the extra sharp cheddar cheese, stir into the milk/flour sauce until melted. Stir in the macaroni.
Pour into a 3 quart baking dish. Top with the remaining extra sharp cheddar cheese.
Bake at 375 F for 30 minutes.