Preheat your oven to 375°F (190°C). Grease a 9-inch square baking pan or a cast-iron skillet.
Peel and cube the sweet potatoes. Bake/Roast them in oven at 400 degrees F until tender, then mash/ mix until smooth. Measure out 1 cup of mashed sweet potatoes.
In a large bowl, whisk together the cornmeal, flour, sugar, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, whisk together the eggs, buttermilk, melted butter, vegetable oil, vanilla extract, and the mashed sweet potatoes until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to over mix.
Pour the batter into the prepared baking pan or skillet. Smooth the top with a spatula. Bake for 22-25 minutes, or until a toothpick inserted into the center comes out clean.
Let the cornbread cool in the pan for about 5-10 minutes before slicing and serving.