How to Make It
Preheat oven to 400°.
Weigh or lightly spoon cornmeal, flours, and potato starch into dry measuring cups; level with a knife. Combine cornmeal, flours, potato starch, sugar, and next 4 ingredients (though baking soda) in a medium bowl; stir with a whisk. Make a well in center of mixture. Combine buttermilk, oil, and egg; stir with a whisk. Add to flour mixture, stirring just until moist.
Pour batter into a 9-inch square metal baking pan coated with cooking spray. Bake at 400° for 25 minutes or until edges are lightly browned. Cool 10 minutes in pan on a wire rack. Serve warm, or cool completely on wire rack.