Heavy cream is a handy thickener for both brown and white pan sauces that are made to order. Most sauces that are finished with cream also include a small amount of butter to smooth the texture and give the sauce an appealing sheen.
In a restaurant setting, where sauces are made to order in small quantities, it is best to pre-reduce certain ingredients, such as the stock, the cream, and sometimes even the deglazing liquid. This, of course, saves time but also improves the flavor of the sauce by avoiding long reduction in the sauté pan. The character of a well-made pan sauce is imparted by the caramelized juices that adhere to the bottom of the pan after sautéing meats or fish. This flavor is lost if it is cooked for more than a minute or two while the sauce is being reduced. Ideally, liquids used for making the sauce should remain in the pan only long enough to dissolve the caramelized juices.