Preheat oven to 375°F (190°C). Spray a 10-inch or heavy oven-proof skillet with cooking oil and set aside.

Sift together flour, cornmeal, baking powder, and salt into a medium bowl.

In a smaller bowl, stir baking soda into buttermilk.

Whisk in sugar, egg, and oil.

Place prepared skillet over medium heat, add butter, and heat until butter melts and starts to sizzle.

Carefully tilt the hot pan to coat sides and bottom with melted butter.

Pour wet ingredients into dry ingredients; combine quickly, using as few strokes as possible.

Scrape batter into the hot skillet.

Bake for 20 minutes, or until golden brown.

Let cool for a few moments before slicing into 8 wedges to serve.