Preheat the oven to 425°F. Place a 9- or 10-inch oven-safe (preferably cast-iron) skillet in the oven while it preheats. Reserve 1 tablespoon of the butter for greasing the pan.
In a large mixing bowl, whisk together the cornmeal, flour, baking powder, salt, and baking soda.
In a separate mixing bowl, combine 7 of the tablespoons butter, yogurt, mashed sweet potato, eggs, buttermilk, and maple syrup. If the butter resolidifies, warm the bowl briefly in the microwave until it melts.
Add the wet ingredients to the dry ingredients and stir until just combined and the batter is thick and lumpy. A few lumps of flour remaining are fine. Fold in the corn.
Carefully remove the skillet from the oven. Brush with the reserved tablespoon butter. Pour the batter into the skillet.
Bake sweet potato cornbread for 18-20 minutes, or until golden brown on top and a toothpick inserted in the center comes out clean.
Let cool for 5 minutes in the skillet. Slice and serve warm right from the skillet, or carefully turn the cornbread out onto a cutting board to cool fully.
Notes
*To make mashed sweet potato, poke one medium sweet potato all over with a fork. Place on a microwave safe plate and microwave for 5-8 minutes (depending on the size of the sweet potato), until easily pierced with a fork, flipping the potato every 2 minutes so it heats evenly. Remove from the microwave and with a knife, carefully slice it open so it can cool more quickly. When cool enough to handle, remove the skin and mash the flesh with a fork or potato masher until mostly smooth (some fibers will remain intact, that’s totally fine).
I haven't tried this, but I think pumpkin or mashed squash could work for the sweet potato.
TO STORE: Refrigerate your sweet potato cornbread in an airtight container for up to 4 days.
TO FREEZE: Store this cornbread for up to 6 months in the freezer wrapped. Let it cool completely, then wrap it tightly in a layer of plastic, then aluminum foil. Thaw overnight in the fridge before serving.
TO REHEAT: Let the cornbread come to room temperature on the counter before serving or reheat it in a 350°F oven until warm.