BREAK UP the lobster shells and place them in a 375F oven to roast for 30 minutes. Transfer shells to a pot, add stock and vinegar. Cover and cook over medium heat for 30 minutes. Remove and discard the shells and reduce the liquid until 1/3 cup remains. Pour the liquid into a bowl and chill. Add egg yolk to the chilled liquid, then beat in the oil. Makes 2 Cups MICHAEL ROBERTS PRODIGY GUEST CHEFS COOKBOOK