I recall reading somewhere that the original Fettucine Alfredo was just
a butter and parmesan coating. However, if you want the cream sauce I
think you're thinking of, why, here's one that should work.
Melt 1/2 stick of butter in a saucepan over low to medium heat. When it
begins to bubble, sprinkle in a tablespoon of flour and mix it in
quickly. Add 1/2 cup heavy cream, some pepper, and 1/4 cup grated
cheese like Parmesan or Pecorino. Stir constantly until thick. This
makes about 1 cup of sauce.
Fry bacon or pancetta bits in saucepan first, drain grease, add butter
Sautee sliced mushrooms and/or onions (with or without the bacon)
Add fresh green peas with the cream
For seafood and cream sauce, sautee quickly scallops, shrimp, crab or
lobster meat in the butter (before adding flour). Add a pinch of nutmeg
with the cream, pepper, and cheese.