Preheat oven to 350 degrees. Grease the edges of an 8X8 cake pan (or similar sized pan) with butter, then line with parchment so it hangs over the edges.

In a large bowl, combine the whole grain flour, spelt flour, baking soda and powder, salt, cinnamon, brown sugar, and white sugar. Whisk to combine.

In a standup mixer or with an electric mixer, combine eggs and buttermilk, then stream in the melted butter. Add the vanilla and bananas and mix until smooth. On a medium speed, add in the dry mixture about 1/4 cup at a time until the batter is smooth, stopping as soon as the dry ingredients are incorporated. Do not over-mix.

Transfer to the cake pan and smooth the top.

Optional: Cut the whole banana in half and sprinkle with remaining 2 Tbsp of sugar. Arrange on top of the batter.

Place the pan on the center rack and bake 350 for 50-60 minutes, or until a cake center is firm and a tester inserted in the middle comes out clean.

Remove from oven and allow to cool for at least an hour before serving.