Roux, a mix of butter and flour, is a component of many French sauces. Basically, it is a way to thicken sauces. You may see it referred to by color—white, blond, or brown—depending on ingredients and how long you cook it. The longer you cook it, the darker it gets. It should be cooked slowly and stirred constantly—a good roux takes time. Every cook should know how to make a basic roux, as it is also the basis for many gravies and soups.

Measure equal weights of butter and flour using a kitchen scale. If you do not have a scale, estimate using these measurements: 1 tbsp. flour equals about 1/4 oz.; 1 tbsp. butter equals about 1/2 oz. So 2 tbsp. flour per 1 tbsp. butter are roughly equal weights. For a basic quantity to feed four as a sauce, start with 2 tbsp. butter and 4 tbsp. flour. For a béchamel sauce (white sauce) for a casserole, double or triple that amount, depending on how much cream sauce you like.

Melt the butter over medium heat. Slowly add the flour, stirring constantly. Continue cooking, stirring constantly, until the roux reaches the desired color. White roux is done when it develops a toasty smell and no longer smells like raw flour. Blond roux is a pale golden color. The longer you cook the roux, the darker it will become, until you reach the light- or dark-brown stage.

Remove the pan from the stove, and transfer the roux to another container to cool. Refrigerate or freeze it in an airtight container. It will keep in the refrigerator for several weeks or indefinitely in the freezer for later use in soups and sauces.

Add milk to a white roux to make béchamel. Use a wire whisk and SLOWLY add 1 cup cold milk to the hot roux. Do not add the milk too fast. Add a little, and whisk until it is fully absorbed before adding more. Once you have added half the milk, pour in the rest, and stir briskly. Cook over low to medium heat, stirring often, until the mixture thickens. Remove it from heat, and stir in nutmeg, salt and pepper to taste.

Flavor a blond (lightly colored) roux with white stock, such as veal, chicken or fish broth, to create velouté. Allow the roux to cool slightly while heating 2 cups chicken stock. It should be very hot but not boiling. Pour the chicken stock into the pan with the roux, and whisk briskly. Return the pan to medium heat, and stir until the liquid is absorbed. Reduce the heat to a low simmer and stir constantly until the sauce becomes smooth. Just before serving, stir in 2 tbsp. light cream. Season to taste with salt and pepper.

For variety, experiment with adding egg yolks, cream, puréed tomatoes, sautéed mushrooms, shallots or wine to your velouté sauce. Or add grated cheese to the béchamel sauce for a creamy cheese sauce.