1. Heat the oven to 325° F. In a blender, combine the sweet potato, spices, maple syrup, eggs, buttermilk, vanilla, and 1/4 teaspoon salt and purée until smooth. Divide the purée among six custard dishes.
2. Put the custard dishes in a large baking pan and pour hot water into the pan until it reaches at least an inch up the sides of the dishes. Bake in the center of the oven for 45 minutes. The custards should be set and barely quiver when shaken. Let cool.
Optional to top with marshmallows and broil until golden.