1/2 cup Madeira
2 teaspoons arrowroot dissolved in 1 teaspoon cold water
1/2 cup beef broth
2 tablespoons finely chopped black truffles (optional)
In a saucepan, heat the Madeira until the mixture is reduced by 1/3. Add the arrowroot mixture, broth, truffles, and salt and pepper to taste. Cook the sauce over moderate heat for 5 minutes (or until sauce is thickened). Stir regularly, being careful not to let it boil.