Preheat the oven to 350 degrees and line with parchment paper and spray a 9×13 pan with non stick spray.
In a bowl, mash the bananas until somewhat smooth. Set aside.
In a mixer, beat the butter on high speed until light and fluffy – about 1-2 minutes. Add both the brown sugar and regular sugar and beat on high speed for another 2 minutes until creamed together. Scrape down the sides of the bowl as needed.
Add the eggs and the vanilla and mix again. Add the mashed bananas to the mixture then beat again on low speed.
In a separate bowl, combine the flour, baking soda, baking powder, cinnamon, and salt. Add the dry ingredients in three additions alternating with the buttermilk and mixing each addition just until combined. Careful not to over mix. The batter will be slightly thick with some lumps.
Spread batter into the pan. Bake for 30-35 minutes. The cake is done when a toothpick inserted in the center comes out clean. Remove the cake from the oven and set on a wire rack. Allow to cool completely.