In a medium bowl add all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Stir with a fork to combine and set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and sugar over med/high speed until light and fluffy, about 2-3 minutes. Add the eggs one at a time, mixing well after each addition. Stop and scrape the mixer to combine. Reduce the speed to medium and add the bananas, followed by the vanilla bean paste and extract and mix to combine. The mixture will look curdled, but that’s the nature of adding mashed bananas to things. Don’t sweat it.
Reduce the mixer speed to low. Alternate adding flour and buttermilk, starting and ending with the flour mixture. Mix until just combined. Remove from the stand mixer and fold once or twice with a rubber spatula. Spread the batter over the prepared banana caramel. Bang the pan a couple of times on your counter to get rid of air bubbles and even out the batter. Place in the oven and bake for about 50 minutes, or until a toothpick placed in the cake comes out clean. Remove cake from the oven and allow to cool for about 5 minutes or so. Run a knife around the sides to loosen the cake a bit and then invert onto a large plate. Allow the cake to cool completely before slicing.
Yields 12 servings.