Preheat Oven: Preheat to 375°F (190°C).
Bake Sweet Potato: Poke holes in the sweet potato, bake on a sheet for 45-60 minutes until tender. Cool, peel, and puree.
Mix Dry Ingredients: Whisk together cornmeal, flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
Combine Wet Ingredients: Mix granulated sugar, brown sugar, milk, sour cream, melted butter, eggs, and sweet potato puree.
Combine Mixtures: Add dry ingredients to wet ingredients, mix until just combined.
Prepare Pan: Pour batter into a greased 10-inch cast iron skillet or baking pan.
Bake: Bake for 30-35 minutes until golden brown and a toothpick comes out clean.
Cool and Serve: Cool in the skillet for 20 minutes before slicing.