Preheat the oven to 350 F. Grease 9 x 2 inch round cake pan. The pan must be 8 cups volume (cake will overflow 8 x 8 x 1 ½ inch square pan, it has only 6 cup volume
TOPPING (for the bottom of the pan):
Combine brown sugar and butter in a bowl. Stir together and then pour into the round cake pan. Spread out evenly with a rubber spatula. Place banana slices directly on top of the butter and sugar mixture.
In a separate mixing bowl combine flour, baking soda, baking powder, pinch of salt, and ground cinnamon. Whisk to combine.
In another separate mixing bowl add brown sugar, sugar, mashed banana, buttermilk, vanilla extract, oil, and eggs. Use a hand mixer to beat and combine.
Add ½ of the dry ingredients to the wet ingredients and use a spoon to start incorporating. Add the remaining dry ingredients and completely incorporate until no white streaks of flour remain. Don't over-mix the batter or your cake will be tough and rubbery.
Pour batter over the top of the sliced bananas. Spread evenly in the pan.
Place in the oven and bake for 45 minutes. Check with a toothpick to make sure the cake is done in the middle and the toothpick is clean when checked. Cook for an additional 3 minutes, or until the toothpick comes clean.
Let cool in the pan for 5-7 minutes. Place a large serving dish on the top of the pan and flip the cake over so that the bananas are on the top of the cake on the serving plate.
Serve warm and enjoy!
The baking pan must be 8 cups volume (cake will overflow 8 x 8 x 1 ½ inch square pan, it has only 6 cup volume)