Preheat your oven to 400°F (200°C). Grease a 9x9-inch baking pan or a 10-inch cast-iron skillet with butter or non-stick spray.
In a large mixing bowl, whisk together the yellow cornmeal, all-purpose flour, light brown sugar, baking powder, baking soda, salt, cinnamon, and nutmeg until well combined and no clumps of sugar remain.
In a separate medium bowl, whisk the sweet potato puree, buttermilk, melted butter, and eggs until the mixture is smooth and emulsified.
Make a well in the center of the dry ingredients and pour in the wet mixture. Use a spatula to gently fold the ingredients together until just combined; do not overmix, as this will make the cornbread tough.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 30 to 35 minutes. At the 20-minute mark, check the color; if the top is browning too quickly, loosely tent the pan with aluminum foil to allow the center to finish setting without burning the crust.
The cornbread is done when a toothpick inserted into the center comes out clean or with just a few moist crumbs. The edges should be slightly pulled away from the sides of the pan.