Preheat oven to 425°.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, cornmeal, baking powder, and salt; make a well in center of mixture. Combine buttermilk, oil, and egg; stir with a whisk. Add to flour mixture; stir just until moistened. Scrape mixture into an 8-inch square baking pan coated with cooking spray. Bake at 425° for 20 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack.