Replacing the Drippings

• Francaise sauce gets its main flavor from chicken drippings, or the juices that render from the skin and meat from chicken during cooking. Chicken drippings comprise rendered fat and liquefied collagen, ingredients you rarely come across in the supermarket -- unless you know what to look for. A less common cooking fat, chicken schmaltz comprises the drippings from the fatty parts of chickens, mainly skin and butcher trim, and is as close as you can get to the drippings leftover from cooking chicken in a pan without actually cooking it. You can find chicken schmaltz in kosher markets and most supermarkets.

Making the Sauce

• To make francaise sauce the night before you serve it, melt about 1 tablespoon of schmaltz for every four chicken breasts you plan on serving it with in a saucepan over medium heat. Add 1 tablespoon of all-purpose flour for every tablespoon of schmaltz you melted. Cook the flour until it develops a blond color, about five minutes. Stir the fat and flour occasionally as they cook. Pour about 1/2 cup of chicken stock and dry white wine in the pan for every tablespoon of schmaltz and simmer until thickened enough to coat the back of a spoon, about 10 minutes, whisking occasionally. Add a couple tablespoons of lemon juice and a couple tablespoons of butter for every couple chicken breasts along with freshly chopped parsley. Lower the heat to medium low and cook the sauce for about 15 minutes, then season to taste with kosher salt and freshly ground black pepper.

Storing the Sauce

• Francaise sauce will keep for two weeks or more in the refrigerator because of the fat and acid in it. Transfer the sauce to a food storage container while it's still warm, then let it cool to room temperature. Scrape the pan using a rubber spatula when transferring the sauce to get the layers that settled to the bottom. Cover the container with its lid and store it in the refrigerator until the next day.

Finishing the Sauce

• Francaise sauce separates into layers as it cools, so you'll open the fridge to find a sheet of butter on top followed by lemon juice, wine and stock mixed with broken-down starch. You have to heat the sauce to 165 degrees Fahrenheit to prevent food-borne illness, but not much over, or the starch will break down and lose its thickening ability. If you don't want to use a thermometer, scrape the sauce and its components into a saucepan and set it on the stove over medium heat. Let the sauce heat until you see bubbles start to form, which means it has reached about 180 F, or just below a simmer. Stir the sauce occasionally as it heats. Lower the heat to low after you see bubbles form. Lightly saute two 1/4-inch-thick lemon slices for every chicken breast and set aside. Cook the chicken breasts and plate for serving. Taste the francaise sauce and adjust the seasoning if needed. Spoon the sauce over the chicken breasts and top each with two lemon slices. Discard any leftover sauce.