My girlfriend and I are huge fettuccine alfredo fans, so we have been trying to recreate one of our favorite Italian dishes at home. The trouble we keep having is thickening the Alfredo sauce without destroying the flavor. We've tried tons of recipes (this one for example: http://www.cooks.com/recipe/ed5dy8k2/easiest-best-homemade-alfredo-sauce.html) but the trouble we keep having is keeping it thick without destroying the flavor. When we are finished with a recipe and remove the sauce from heat, it never seems to thicken up. It just stays a kindof milky consistency and gets cold ):
Reduce the liquid first before adding the cheese. My favorite recipe is to reduce heavy cream by half and then add in plenty of grated Parmesan. Some people add Romano, butter, and/or nutmeg as well.
Sauces can be reduced using the pasta itself as a thickening agent.
For alfredo, make the sauce in a large pan, then add cooked and drained pasta and toss together over a medium flame until reduced.
Two things happen in this technique: the starchiness of the pasta itself helps to thicken the sauce, and the pasta absorbs some of the sauce.