Step 1

Preheat an oven to 350 F. Butter a 9- by 12-inch glass baking dish.

Step 2

Bring a large pot of water to a boil over high heat. Add the sweet potatoes and cook until soft, about 12 minutes. Drain the potatoes and transfer to a large bowl. Add the butter and mash the potatoes with the butter. Stir in the flour, brown sugar, baking powder, cinnamon, nutmeg, allspice and 1 teaspoon salt until well blended. Fold in the crushed pineapple and transfer to the prepared baking dish.

Step 3

Bake until the sweet potatoes are brown on top, about 30 minutes Remove from the oven and place the marshmallows in a single layer on top.

Step 4

Preheat the broiler and place the dish underneath the broiler to toast the marshmallows. Watch carefully as they will toast very fast!