One of the five French mother sauces, you can use a white sauce, or bechamel sauce, in a number of baked dishes. The sauce serves as the base for baked macaroni and cheese, for example. The amount of liquid you add determines how thick the finished sauce is. A thicker version of white sauce acts as the base for souffles, too. You can dress up a basic white sauce by adding herbs, spices or aromatics to it or leave it plain.
Place the butter or olive oil in the saucepan on the stove, over medium heat. After the butter melts or the oil heats, you can add the shallot or onion if desired, to give the sauce some flavor. Let the aromatics cook for a few minutes.
Add an equal amount of flour to the pan and whisk to form a paste, called a roux. The longer you let the butter and flour mixture cook, the more complex the flavor becomes and the darker the sauce will be.
Pour the milk into the saucepan and whisk to combine. For a thick sauce, use a small amount of milk, such as 1 cup if you used 2 tablespoons each of butter and flour. Double the amount of milk for a thinner, pourable sauce.
Add seasoning to the sauce if desired, such as a bay leaf or dried thyme.
Let the sauce simmer until it is thickened. Remove any big pieces of dried herbs, such as the bay leaf, before using the sauce in a recipe.