Whisk dry ingredients, white whole wheat flour, baking powder, salt, and cocoa in a large bowl until uniform. Whisk wet ingredients, maple syrup, warmed coconut oil, greek yogurt, vanilla, egg, milk and coffee in a second bowl until uniform and emulsified. Add wet ingredients to dry and stir to combine.
Pour batter into a prepared 8x8 pan and bake for 30 minutes or until a toothpick inserted into the middle comes out clean.
A few minutes before removing the cake from the oven, combine ingredients for Maple Butter Sauce in a glass jar or other microwave safe bowl. (The jar is just handy because you can put the lid back on and stick any leftovers in the fridge!) Heat in the microwave for 30 seconds, stir. Heat for another 30 seconds, stir. Continue just until the sauce begins bubbling up. As soon as it does, stir well and you are done. Be careful the jar will be hot!!
Top the whole cake, or individual slices with sauce and serve warm. Leftovers are also moist and chocolaty and delicious... not that you will have much in the way of leftovers. Enjoy!