A part of every seder, haroset is a thick condiment that symbolizes the mortar the Jews prepared when they were slaves in Egypt. Recipes vary but typically include fruit, nuts, and honey. The marshmallows are a relatively new addition; you can find kosher-for-Passover marshmallows in supermarkets. Use the grating attachment on a food processor to quickly shred the apple. Prepare this up to a day in advance.