Preheat oven to 425 degrees, place cast iron skillet into oven while it is preheating
Melt butter, save about 1 tbsp
Mix all dry ingredients into one bowl (cornmeal, flour, sugar, salt, baking powder, and baking soda)
Mix all wet ingredients into a separate bowl (butter, milk, buttermilk, and eggs)
Pour wet ingredients into dry ingredients and mix well
Take skillet out the oven and pour reserved melted butter and coat skillet
Add cornbread mixture to the skillet
Reduce heat to 350 degrees and put cornbread into the oven
Cook for 20-25 minutes