Combine cornmeal, self-rising flour, mayo, buttermilk, butter, and eggs in a medium bowl. Add a little water to get the right creamy consistency as you mix.
Add vegetable oil into the cast iron skillet, then spread it evenly in the skillet using a paper towel, removing any excess oil. Sprinkle a teaspoon of cornmeal over the oil then, pour the cornbread mixture into the cast iron skillet spreading it evenly.
Bake uncovered for about 25 minutes until golden brown. Serve warm with butter and your favorite meal.