Make this up to 1 week ahead, cover and refrigerate, and thin with more broth if necessary when reheating.
1. Melt margarine in medium skillet over medium-high heat. Add sliced mushrooms and a dash of salt and pepper; cook, stirring often, 4 minutes, or until golden. Add sherry, and cook 30 seconds, stirring constantly.
2. Whisk broth and cornstarch in small bowl to blend. Add mixture to skillet, and bring to a boil, stirring constantly. Reduce heat to medium; cook 1 minute.