How to Thicken Alfredo Sauce
Homemade alfredo sauce will thicken as it simmers and cools. So, try cooking it a little bit longer if it is not thickening to your liking.
However, if it is still too runny, stir in extra grated Parmesan cheese. Or, if the sauce is cheesy enough for your taste, feel free to incorporate a cornstarch slurry. Just whisk equal parts cornstarch and cold water (about one tablespoons of each) in a small bowl. Then, mix a teaspoon or two of the mixture into the sauce, and let it cook for about a minute to thicken.
How to Thin Alfredo Sauce
If the sauce thickens too much, whisk in an extra splash of heavy cream, reserved pasta water, or chicken broth. Just heat the sauce on the stove, stirring consistently, until warmed through.
