Flank Steak With Mustard-Caper Sauce
["4 Tbsp. butter or margarine", "1 Tbsp. salad oil", "1 (about 1 1/2 lb.) flank steak", "3 Tbsp. dry vermouth or dry white wine", "1 Tbsp. Dijon mustard", "1/4 tsp. Worcestershire", "1 1/2 Tbsp. capers, drained well", "watercress (optional)"]
["Melt 1 tablespoon of the butter with the oil in a wide frying pan over medium-high heat.", "Place meat in pan and cook, uncovered, until meat is browned on both sides but still pink in center when slashed (5 to 6 minutes total)."]
["butter", "salad oil", "flank steak", "white wine", "mustard", "Worcestershire", "capers"]