Preheat the oven to 350℉. Grease a 9X9-inch pan with non-stick cooking spray and line it with parchment paper.
In a large bowl using an electric handheld mixer, cream together the butter and sugar on high until fluffy. Add the egg, vanilla, mashed bananas, and sour cream and continue beating on medium until fully combined.
In another bowl, whisk together the flour, baking soda, baking powder, and salt. Add to the wet ingredients and beat on low just until all the flour mixture is incorporated.
Mix together the brown sugar, cinnamon, and chocolate chips to make the filling/topping. Spread half of the batter evenly into the prepared pan and sprinkle half of the filling mixture on top. Then, gently spread the rest of the batter on top, and lastly, sprinkle on the last of the topping.
Bake in the preheated oven for 30-35 minutes or until a toothpick inserted into the center comes out clean. Let cool for at least 30 minutes before serving. Enjoy!
Notes
Unsalted butter may be used instead with an additional ¼ teaspoon of salt added to the recipe.
You may use plain unsweetened yogurt in place of sour cream.
Store leftover cake in an airtight container at room temperature for up to 3 days.