Liaison sauces are ones in which a particular ingredient is the thickening agent. The liaison may be a gelatin—a water-soluble protein in meat and fish that, when present in a liquid, gives the sauce a lovely, syrupy texture. Or it may be butter—a particularly popular choice in recent years for its ability to create a silky, rich sauce. Believe it or not, even animal blood and coral (shellfish roe) can be used to thicken sauce.
There are numerous other sauce-thickening liaisons, including cream, cheese and yogurt. But perhaps the most common thickener in American cooking is flour, used in the classic sauce called béchamel.
Cooks have been using flour to make sauces since the seventeenth century, when roux was introduced (and went on to become the primary sauce thickener of Western chefs, until the late 20th century). Flour--as well as other starches like arrowroot and cornstarch--thickens sauces because it has large molecules that loosen in a liquid and bond with that liquid. The starch becomes suspended in the liquid, creating a viscous sauce.
Flour has long been the home cook’s thickener of choice in part because it is inexpensive and creates a stable sauce—one that won’t break down easily. And unlike arrowroot and cornstarch, which give sauce a shiny look, flour produces a pleasant matte appearance. Flour is readily available in the home kitchen pantry, and sauce makers turn to it to make gravy, to thicken stew, and to make the long-popular home-style sauce, béchamel.
Béchamel is a rich-textured, deeply satisfying sauce used in creamed dishes, vegetable gratins and other preparations in which its relatively neutral flavor is desirable. Milk, or sometimes a combination of milk and cream, is the main ingredient—thus it is of prime importance that it be the real deal: high-quality, nutrient-dense organic milk and cream. After all, as one of the great “mother sauces” in French cuisine, béchamel deserves to be made with milk that comes from the best “mothers” in the farm field.
To prepare béchamel, begin with the roux: Melt the butter over medium-low heat, then stir in the flour until smooth. Cook the roux for a few minutes, stirring it occasionally, to cook out the raw flavor of the flour.
While the roux is cooking, heat milk or cream over a low flame until it comes to a simmer. (Cold milk or cream may also be used, but will require vigorous whisking, when added to the roux, to prevent the formation of lumps).
After letting the hot roux cool for a brief moment, whisk the simmering milk or cream into the roux. Keep whisking as you bring the sauce to a simmer. Now reduce the heat to low and cook for at least ten, and up to forty minutes, skimming the sauce if it forms a skin. This additional simmering helps cook the rest of the floury taste out of the sauce. (If you are making a béchamel based on soy milk or soy cream, however, do not cook it longer than a few minutes.) The final step is to season the béchamel with salt and pepper.
Although béchamel in this simplest form is purposely neutral-tasting, you can give it complexity by adding herbs, spices, meat or fish, depending on how you would like to accent the finished dish. Onion-accented béchamel is called soubise, while sauce Mornay features cheese. You can also create sauce crème, a richer-style béchamel, by using heavy cream in it.
Creamed Smoked Salmon on English Muffins - Want to serve something special, but you don’t want to break the bank? A little smoked salmon will go a long way when you combine it with an organic béchamel sauce and spike it with colorful green onions.
Vegan Broccoli Gratin – Got a broccoli skeptic in the family? There’s something about suspending broccoli in a creamy sauce that makes a convert out of a doubting Thomas.