Caviar-Champagne  Sauce Sauce Ingredients (Beurre Blanc) : 1 Tbsp. (1/8 stick) unsalted, chilled butter, cut into 8 pieces 1/2 Tbsp. unbleached, all-purpose flour 1/4 c. Champagne or other dry, good-quality, sparkling white wine 1/8 c. low-sodium chicken broth 1/16  tsp. (a pinch) Dijon mustard (liquid, not powdered form) 1/2 tsp. fresh