Prepare the sweet potato: Wrap sweet potato in aluminum foil and roast for 1 hour at 425F in an oven or toaster oven. It’s done when it can easily be pierced with a fork. Allow the sweet potato to cool. Then, mash the sweet potatoes using a fork, making sure to break up any long strings of sweet potato. Measure out 1.5 cups. Set aside.
Preheat the oven to 375°F. Grease a 10-inch cast iron skillet with butter and set it in the oven on the lower middle rack.
In a large bowl, whisk together the dry ingredients.
In a separate bowl, combine mashed roasted sweet potato, eggs, milk, maple syrup, and vanilla. Whisk to combine well. The mixture should be smooth and thick.
Using a rubber spatula, combine the dry ingredients with the wet ingredients. gently fold the sweet potato mixture with the cornmeal mixture just until no dry streaks of flour remain. Do not over-mix.
Place preheated/greased skillet on a heat-safe surface. Scrape batter into skillet, evening out the top into the edges.
Bake for 25-30 minutes or until the top is puffy and golden brown. There should be cracks visible around the edges of the cornbread.
Let the cornbread cool for 5-10 minutes in the cast iron. Then, slice and serve with butter. Enjoy!