Alfredo sauce is really easy, it's a calorie bomb though. It's just one pint of heavy whipping cream, a stick of butter, a cup of grated parmesan, salt, and garlic powder to taste. Parsley makes a nice addition too. The trick with cheese sauces is not to get it too hot or it can break. You heat up the cream and butter then slowly stir in the cheese a little at a time. A teaspoon of corn starch in a slurry helps thicken and emulsify the sauce, as does a 1/2 teaspoon of sodium citrate, but they aren't necessary.

Pasta water, particularly if you don't use a lot of excess water when cooking the pasta, can be used in place of the corn starch slurry, but it can also add a lot of salt so you have to be careful with that.