Preheat the oven to 375 degrees F.
In a large bowl, whisk together the cornmeal, flour, brown sugar, baking powder, baking soda, salt and pumpkin pie spice.
In a separate, medium bowl, whisk together the mashed sweet potatoes, eggs, buttermilk, honey and butter. Add the wet ingredients to the dry ingredients, and stir until just combined.
Pour the batter into a cast-iron skillet; use a spatula to smooth to an even layer if needed. Place in the oven and bake until golden brown and a toothpick inserted in the center comes out clean, about 35 minutes. Serve the cornbread in the skillet.