1. Heat oven to 425 degrees. Rinse turkey breast; pat dry. Rub breast with salt and pepper.

2. Strew roasting pan with onions, carrots, and celery; set turkey over vegetables. Roast until breast is cooked through, about 1 1/2 hours; interior temperature should be about 170 degrees.

3. Cut breast in half; transfer one half to a cutting board, tent with foil to warm, and set aside. Reserve other half for later use.

4. Place roasting pan over two medium-hot burners on range. Sprinkle cooked vegetables and drippings with flour, and cook, stirring constantly, until flour forms a golden-brown film over bottom of roasting pan and vegetables are completely coated with film and turkey drippings, 2 to 3 minutes. Do not let pan get too hot, or drippings will burn.

5. Pour Madeira slowly into pan, and cook, scraping up film from pan with a wooden spoon until a thin paste forms, about 1 minute. Slowly add stock, stirring, until paste thins to a thick liquid. Continue adding stock, stirring, until gravy is desired consistency. Season to taste with salt, pepper, and a splash more Madeira, if desired. Strain gravy, pressing down on solids with a rubber spatula to extract juices and flavor. Discard solids; transfer gravy to the top of a double boiler to keep warm, or let cool and refrigerate.