Sweet potatoes were brought to the New World when colonists came over from Europe. Recipes for mashed sweet potato or “sweet potato pudding” have been around since the 1700s. Marshmallows became popular in the early 1900s, and a recipe book published by a marshmallow company in 1917 included a recipe for a sweet potato pudding topped with marshmallows. The recipe became an instant hit, and as it was passed down from generation to generation, it became an American Thanksgiving holiday tradition.