Cut cold roast lamb in thin slices. Cook five minutes two tablespoons butter with one-half tablespoon finely chopped onion. Add lamb, sprinkle with salt and pepper, and cover with one cup Brown Sauce, or one cup cold lamb gravy seasoned with Worcestershire, Harvey, or Elizabeth Sauce. Cook until thoroughly heated. Arrange slices overlapping one another lengthwise of platter, pour around sauce, and garnish with toast points. A few sliced mushrooms or stoned olives improve this sauce.