Every Thanksgiving in Natchez, Mississippi, my aunts and uncles, a herd of cousins, and the occasional neighbor end up at my grandmother's house for dinner. There are far too many of us for a sit-down affair, so we all get in line, plates in hand, and fuel up at the sideboard, which is crammed with the standard holiday fare. I make a polite effort to balance my mom's cranberry salad with my aunt's buttery rolls—but it's Grandmother's sweet potato casserole that inevitably upsets the balance. I can't help but pile on spoonful after spoonful, burying the turkey and pushing the stuffing perilously close to the edge. I happily forgo the green beans.
My grandmother, Sarah Tillman, has been making this type of casserole since the 1940s. She's tinkered with it over the years, but she's confident that sometime in the '50s—probably the first time her in-laws came to dinner—she got the mix right. She starts with fresh, not canned, sweet potatoes. The kind she favors, which are about the size of baking potatoes, have smooth skin and either white or deep orange flesh. Yams, to set the record straight, are monocotyledons (plants that sprout from a single-leaved embryo) that originated in Africa or Asia. They come in many shapes, and most have a hairy, barklike coating and white or yellow flesh. Sweet potatoes are dicotyledons (from a two-leaved embryo), native to Central America, and often sweeter than yams.
As if sweet potatoes weren't already sweet enough, Grandmother doctors them with pecan pieces, pineapple chunks, and plump raisins soaked in sherry, and tops it all with a layer of marshmallows, which turn all brown and gooey and transform an otherwise mushy melange into one of my all-time favorite dishes. Grandmother believes sweet potatoes and marshmallows "just belong together", but this is not news. _Good Housekeeping _proposed the combination in 1922 with Sweet Potatoes de Luxe, a recipe that called for "wreaths of marshmallows" as well as the requisite pieces of pineapple.
Grandmother doesn't put ginger or Grand Marnier in her casserole—although she has seen recipes calling for these elegant (but fussy) additions. Recently, however, she made a fortuitous discovery in her modest but much-loved The McCormick Spices of the World Cookbook (McGraw-Hill, 1964). "There it was! My sweet potato recipe, all printed out!" she exclaims. "It made everything so much easier!"