Bake the sweet potato on a baking sheet in the oven on 400 degrees for about 1 hour or until soft. Remove the skin and transfer the pulp to a food processor. Process until smooth.
Increase the heat to 450 degrees.
Pour 2 Tbsp. oil in a 9-inch cast iron skillet. Heat in the oven for 5 minutes.
Combine the sweet potato purée, egg, buttermilk, milk, and oil in a medium bowl. Whisk until combined. Add the cornmeal, baking powder, salt, cinnamon, and cayenne. Stir until combined. Pour the batter into the hot skillet.
Bake for 22-25