Use Cold Butter to Make Creamy Pasta Sauce Better
One of the tricky parts of creamy pasta sauce is that the sauce may stray or become too runny. The emulsion (a mixture of fat and liquid) does not hold. This can be avoided by using cold oil in the sauce.
Chef Mario Batali shares this tip among the ten most important pasta cooking tips. The reason for the low temperature: Heat (as in a warm paste) can upset the delicate balance between fat and liquid in the emulsion. If you use cold butter, you are less likely to get too hot and get a better emulsion.
This is true for other emulsion sauces, says Fine Cooking , such as Hollandaise sauce.
10 Most Important Tips for Cooking Pasta | Mario Batali