To Bake the Sweet Potato: Preheat oven to 425°F. Scrub skin of large sweet potato. Place on a pan and bake for 40-50 minutes or until fork tender. Cool for 20 minutes, then peel and puree. Let cool.
Preheat oven to 375°F. Butter the bottom and sides of a 10-inch skillet or similar. Set aside.
In a large bowl, use a whisk to sift together cornmeal, flour, granulated sugar, brown sugar, baking powder, baking soda, salt and pumpkin pie spice.
In a separate medium bowl, whisk together mashed sweet potato, milk, sour cream and eggs. Stir to combine, then whisk in melted butter.
Add the sweet potato mixture to the dry ingredients, stir until fully moistened.
Pour the cornbread batter evenly into the prepared skillet, Sprinkle the top with turbinado sugar, if using.
Bake for 40-45 minutes just until a toothpick inserted into the center comes back clean and the top is lightly golden brown.
Serve with butter, drizzled with maple syrup or honey.