1. 1. Preheat and Prepare the Skillet: Place a 10-inch cast iron skillet in your oven and preheat the oven to 400 F (200 C). Allowing the skillet to heat up with the oven is crucial for achieving that wonderfully crispy bottom crust.

2. 2. Combine Dry Ingredients: In a large mixing bowl, whisk together the cornmeal, all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed.

3. 3. Mix Wet Ingredients: In a separate medium bowl, whisk together the active sourdough starter, buttermilk, melted butter, and eggs until well combined. The mixture should be smooth.

4. 4. Combine Wet and Dry: Pour the wet ingredients into the bowl with the dry ingredients. Stir gently with a spoon or spatula until just combined. Be careful not to overmix; a few small lumps are perfectly fine. Overmixing can lead to tough cornbread.

5. 5. Pour into Hot Skillet: Carefully remove the hot cast iron skillet from the oven using oven mitts. If desired, you can add a tablespoon of butter to the hot skillet and swirl to coat, or simply pour the batter directly into the hot, ungreased skillet. The heat will immediately start to cook the edges.

6. 6. Bake Until Golden: Return the skillet to the preheated oven and bake for 25-30 minutes, or until the cornbread is golden brown on top and a wooden skewer or toothpick inserted into the center comes out clean.

7. 7. Cool Slightly and Serve: Once baked, carefully remove the skillet from the oven. Let the cornbread cool in the skillet for about 5-10 minutes before slicing and serving. This allows it to set and makes for easier slicing.