Preheat oven to 400°. In a large bowl, combine flour, cornmeal, sugar, baking powder, baking soda and salt. In a small bowl, whisk egg, sour cream, milk and butter; stir into dry ingredients just until moistened.
Pour into a greased 8-in. square baking dish. Bake 20-25 minutes or until a toothpick inserted in center comes out clean. Serve warm.