Sweet potatoes have been popular in the American South since colonial times, when slaves who worked in plantation fields and kitchens mistook them for the yams they knew in their homelands. “The tropical region of Nigeria, the Ivory Coast, and West Africa is called the ‘yam belt,’” said Frederick Opie, Ph.D., Professor of History and Society at Babson College in Boston. “When Africans came to the new world as enslaved people, they substituted sweet potatoes for yams.”
The Southern classic of sweet potato pudding or “pone” was popular as either a side dish or dessert, and by the end of the Civil War, appreciation of the orange tubers had migrated to the North. Sweet potato pie is mentioned in an 1887 issue of Godey's Lady's Book, a Philadelphia women’s magazine edited by an ahead-of-her-time woman named Sarah Josepha Hale (who also wrote “Mary Had a Little Lamb” and is generally considered to be “the godmother of Thanksgiving” because she lobbied government officials to have it declared a national holiday).
Candied sweet potatoes appeared in the first edition of the "Boston Cooking School Cookbook" in 1896. “Sugar was still a luxury item, associated with holidays and special occasions,” said Opie. But nobody thought of crowning their casseroles with marshmallows for a few decades. The 19th century French had whipped egg whites and sugar with sap from the roots of Althaea officinalis -- the marshmallow plant -- but these confections were prohibitively expensive until the substitution of gelatin for the plant extract allowed for mass production. In 1917, a company called Angelus Marshmallows distributed a booklet of recipes that utilized the frothy white puffs, and a classic culinary marriage began.
A 1929 cookbook called "Vital Vegetables" is considered the first to include a recipe for the dish -- ideal timing since the ingredients were cheap during the Depression era in America. Some people consider the idea a travesty, including Cathy Kaufman, president of the Culinary Historians of New York. “But certainly marshmallows moved from a handmade process to a commercial product in the 1920s,” she said, “so this all makes sense, part of the idea that commercial products are modern and progressive.” Although the dish has a place of honor on many Thanksgiving tables, it continues to be a source of opposing opinions that rivals Democrat vs. Republican politics.
Watch how to make this favorite Thanksgiving casserole (with marshmallows!):