Preheat the oven to 350° F.
Prepare a 8 x 8 glass baking dish with a vegan margarine or oil, set aside.
Measure the plant based milk in a one cup measuring cup, stir in the apple cider vinegar, and set aside to curdle, this is a vegan buttermilk.
In a small mixing bowl, mix together the flours, cocoa, baking soda, baking powder, instant espresso powder, and salt.
*Can't find oat flour? Make your own, add the oats to a high speed blender and blend until you have the consistency of a flour.
Next add the maple syrup, apple sauce, oil, vegan buttermilk, and the vanilla.
Stir until well combined, pour into the greased dish.
Place into the oven and bake for 30 minutes.
Check the cake with a tooth pick, if it comes out clean it is done, if not return to the oven for another 15 minutes.
Baking times can vary, check the cake at 30 minutes and then again about every 5 to 10 minutes until done.
Once the cake is done, remove from the oven and place on a cooling rack until completely cooled before frosting.
*Note: Do not make the frosting until the cake is completely cooled.