For the cake:
Preheat an oven to 350°F. Grease a 9x13 pan.
In a bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.
In a second bowl with a whisk together the melted butter and sugar.
Add the eggs one at a time, mixing well after each addition, then mix in the vanilla and bananas.
Add the flour mixture in 3 additions, alternating with the sourcream in 2 additions, mixing until just combined; scrape down the sides of the bowl as needed. Whisk until no traces of flour remain, about 30 seconds; do not overmix.
Pour the batter into the prepared pan and smooth the top. Bake in the preheated oven on a center rack for about 45 minutes until a toothpick inserted comes out with just a few moist crumbs.
For the cream cheese frosting
Combine the butter and cream cheese in the bowl of your stand mixer.
Add the confectioner sugar, one cup at a time. Mix on low until combined.
Add vanilla and mix until combined
Mix on medium sped until smooth and creamy.