Preheat the oven to 350°. Grease an 8-inch square baking pan.
In a large mixing bowl combine the oil, eggs, and buttermilk. Whisk to blend.
Add the flours, cornmeal, sugar, baking powder, and salt. Mix well.
Pour the batter into the prepared pan and bake for about 30 minutes or until golden and a tester inserted comes out with a few crumbs attached.
To make as a mix: Take a large ziptop bag or container and label it with the wet ingredients and the baking instructions. Measure out the dry ingredients into the bag. Seal and store until ready to use. Freeze for longest shelf life.