Preheat oven 350 degrees F. and grease a 9x13 inch baking dish with non-stick spray
In a large bowl combine cornmeal, flours, sugar, baking powder, powdered buttermilk, and salt.
Add the wet ingredients and stir till just combined
Pour the batter into the prepared baking dish and bake in preheated oven for 45 minutes or until the cake browns and begins to show cracks
Cool slightly before slicing