Cooking is not rocket science. Or brain surgery. Or rocket surgery, for that matter. Good cooking does not necessitate a laundry list of exotic ingredients or the possession of intricate technique. In fact, the best alfredo sauce I've ever made (or eaten) consists of three very simple ingredients: butter, heavy whipping cream and Parmesan cheese.
Although I firmly believe recipes are guidelines (except when baking, when it's actually a formula), some ingredients cannot be substituted for optimal results. When I say butter, I mean real butter. Not margarine, not I Can't Believe It's Not Butter (I actually can believe it's not butter), not some other butter substitute. When I say heavy whipping cream, I don't mean Half & Half, or milk, or, heaven forbid, skim milk.
I would not recommend substituting anything for this recipe. If you're on a diet, then your best bet would be to find another recipe, because this is full fat, full flavor deliciousness.
You will need roughly equal parts butter and heavy whipping cream. The amount will depend on how much alfredo sauce you expect to use. I would not recommend making much more than you need since this does not keep and/or reheat well.
Melt the butter in a sauce pan over medium heat. Add the whipping cream and heat almost to a boil. Boiling and dairy products can create an experience you would not wish to repeat. Slowly stir in parmesan cheese until a thin gravy consistency is reached. During this step, make sure to stir constantly so as not to burn the cheese and also to ensure the cheese is incorporated enough to create a creamy smoothness.
Now, ladle over your favorite pasta (fettuccine is my recommendation) and enjoy. That, by itself, is enough, but embellishments are definitely encouraged.
A grilled (or baked) chicken breast seasoned with basil, garlic and oregano can be sliced or diced and added to the plate.
My favorite embellishment involves a bit more technique, which can also be applied to the basic preparation.
Sautee a few sliced mushrooms in butter and a splash of white wine until softened. Then add some fully cooked diced ham and lemon pepper to taste. Then add heavy whipping cream (roughly the same amount as the butter) and heat through. Add fully cooked and cooled noodles (again fettuccine is preferred). Stir and heat through. Add parmesan cheese to desired consistency, stirring constantly. When your preferred consistency and creaminess is reached, transfer immediately to plate and enjoy.