Preheat oven to 400°F.
Grease an 8-inch cast iron skillet.
In a medium bowl, whisk together the flour, cornmeal, baking powder, baking soda and salt.
In a small bowl, whisk together the buttermilk, oil, egg and sugar.
Pour the buttermilk mixture into the flour mixture and stir just until combined (do not overmix).
Pour the batter into the prepared skillet.
Bake for 18-20 minutes, until golden brown and a toothpick inserted in the center comes out clean.
Allow to cool for 5 minutes before slicing and serving.