Put butter, ghee, or coconut oil in the cast iron or oven proof skillet and in the oven to melt while the oven is preheating.
Mix the flour, cornmeal, sugar, baking powder, and salt in a bowl.
Add the milk, sourdough starter, and the beaten eggs to the dry ingredients and mix well.
Take the skillet out of the oven and pour the melted fat into the batter and mix well.
Pour the batter into the hot skillet and smooth the top.
If you are using a baking dish instead, make sure to grease the sides and bottom so it doesn't stick.
Bake for 25-30 minutes until golden brown and a toothpick inserted in the middle comes out clean.
You can serve it straight from the pan if you want to. I like to put a plate over the top of the skillet and turn it over so that the cornbread is on the plate and serve it from there.
Cut it into wedges, slather on some butter, and serve warm.