Preheat the oven to 375°F. Lightly grease a large cast iron skillet with vegetable shortening or vegetable oil.
Whisk together the cornmeal, flour, baking powder, salt, cinnamon and allspice. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment or large mixing bowl, beat the sweet potatoes, eggs, yogurt, dark brown sugar and butter. Mix until combined.
Alternate adding the dry ingredients and buttermilk until fully mixed. Do not overmix. The sweet potatoes may still be a little chunky.
Pour the batter into the prepared cast iron skillet. Bake for 30-35 minutes. Test using the toothpick test.
If you've tried this recipe, come back and let us know how it was in the comments or star ratings!
Notes
The average sweet potato is about 3/4 cup mashed. They come in so many shapes and sizes. I usually buy two medium sweet potatoes and then cook them in the microwave.