Cook your pasta according to package instructions, preferably al-dente. Set some pasta water aside.

In a large saucepan on medium heat, add butter. Once melted add flour. Whisk and cook for a couple minutes to cook the flour taste out.

Add milk, salt, pepper, and garlic. Whisk until it is thick. Remove from heat and stir in cheeses.

Stir in cooked fettuccine until it is all coated in the Alfredo sauce. If it is too thick add some of the reserved pasta water. Serve immediately and garnish with parsley.