Bring to room temperature: Remove the eggs and buttermilk from the refrigerator and let them come to room temperature while you prepare the sweet potatoes.
Cook the sweet potatoes: Add the cubed sweet potatoes to a medium saucepan, cover with water, and bring to a boil over high heat. Cook for about 15 minutes, or until fork-tender.
Drain and mash: Drain the water and mash the sweet potatoes in the pot until smooth. If the sweet potatoes are extra stringy, transfer to a blender or food processor and puree until smooth. Measure 1 cup of mashed sweet potato and set aside to cool slightly.
Preheat your oven to 350°F (177°C).
Mix the dry ingredients: In a large mixing bowl, whisk together the cornmeal, flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Mix the wet ingredients: In a separate bowl, whisk together the buttermilk, eggs, brown sugar, melted butter, and 1 cup of mashed sweet potato until smooth and well combined.
Heat the baking pan: Place a 5x8-inch or 9x13-inch baking pan in the preheated oven for 3–5 minutes, or until the pan is hot.
Combine: As the pan heats, add the dry ingredients to the wet ingredients and fold gently until just combined. Do not over mix.
Grease the baking pan: Carefully remove the pan from the oven and add the 1-2 tablespoons of butter. Carefully swirl to coat the bottom of the pan with the butter as it melts. Once the pan is coated, pour the batter into the prepared pan and spread evenly.
Bake for 35–40 minutes, or until a toothpick inserted in the center comes out clean. (If using a 9x13-inch pan, begin checking for doneness around 30–35 minutes.)
Cool and serve: Let the cornbread rest for 10 minutes before slicing. Serve warm with whipped honey butter, if desired.