BREAK UP the lobster shells and place them in a 190ºC 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 one third 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