1 (2-1/2 pound) sirloin steak, 1-1/2 inches thick
1/2 cup butter or margarine
1/4 cup chopped fresh parsley (or 4 teaspoons dried)
1/4 cup finely minced onion
2 tablespoons Worcestershire sauce
1 teaspoon freshly ground coarse pepper
1/2 teaspoon dry mustard
Lightly score edges of steak at 1-inch intervals. Preheat grill or broiler.
Combine butter, parsley, onion, Worcestershire sauce, pepper and mustard in a small saucepan. Heat stirring continually, over low heat, until butter melts. Reserve 1/4 of the mixture.
Place steak on grill or broiler pan. Brush steak with butter mixture. Cook, basting frequently with butter mixture, about 6 minutes per side for medium.
Place steak on a serving platter. Cut into thin slices across the grain. Drizzle reserved butter mixture over steak and serve.