Ingredients:
¼ cup butter
1 clove garlic, crushed, finely grated, or pressed (optional)
1 cup heavy cream
1½ cups freshly grated Parmesan cheese (or you could use half Parmesan and half Romano*)
Salt & pepper to taste
Pinch of freshly grated nutmeg (optional)
¼ chopped fresh parsley (for garnish)
Directions:
Melt butter in a saucepan or skillet over medium low heat. If you’re flavoring the sauce with garlic, add it to the melted butter and cook for about 1 minute. Do not let it brown.
Whisk in the cream and simmer gently for 5 minutes to cook out some of the water from the cream.
Remove the pan from heat and add cheese a handful at a time, whisking after each addition until the cheese is melted.
Return the pan to the heat and let the sauce simmer gently for 4 to 5 minutes more until the sauce is thickened. Do not let the sauce boil or else it will separate and lose its smooth texture. Season with salt and pepper and add a pinch of freshly grated nutmeg (optional), because nutmeg is heavenly in cream sauce.
If you’re cooking pasta: When your pasta is cooked al dente, drain it well (do not rinse it) and toss it in the skillet with the hot Alfredo sauce. Garnish with parsley and serve immediately.
*Do not use pre-grated cheese; it’s coated with a substance that inhibits smooth melting and will ruin the texture of your Alfredo sauce.
How to Thicken Alfredo Sauce 5 Ways
Add more cheese. Remove the sauce from the heat and whisk in another handful of grated cheese until it’s melted. Return the sauce to the heat source and heat very gently without boiling.
Add cream cheese. This recipe for Cream Cheese Alfredo shows you how to do it.
Make a roux of butter and flour, as in this recipe for Buttery Alfredo Sauce.
Use cornstarch. If you use low-fat ingredients to make Alfredo sauce, you can thicken it with a teaspoon of cornstarch, as in this recipe for Fettuccine Alfredo II.
Add egg yolk, as in this recipe for Fettuccine Alfredo V. To keep the yolk from scrambling, temper it by whisking in a little hot cream, then add the yolk and cream mixture back to the sauce.
Source: https://www.allrecipes.com/article/how-to-make-alfredo-sauce/