Mix the batter: Add all the ingredients (cornmeal, flour, sugar, baking powder, salt, milk, egg, and oil) to the cast iron skillet, and using a medium whisk, gently whisk together until combined.
Bake: Bake the cast iron skillet in the oven for 20-25 minutes or until golden. To test for doneness: Insert a toothpick or a butter knife in the center and it should come out clean.