01 -
Preheat oven to 350°F (175°C). Line an 8×8-inch pan with heavy duty aluminum foil and spray with cooking spray; set aside.
02 -
To a large saucepan, add butter, brown sugar, and heat over medium heat to melt butter. Whisk or stir constantly to combine the sugar into the melting butter. Allow mixture to come to a boil and boil for 30 to 45 seconds. Pour sauce into the prepared pan. Add the banana slices in an even layer over the sauce, leaving about 1/2-inch space between slices. Set aside.
03 -
To a large bowl, add egg, brown sugar, granulated sugar, oil, sour cream, and vanilla extract, and whisk to combine. Add the mashed bananas and stir. Add flour, baking powder, baking soda, and salt, and stir until just combined. Do not overmix.
04 -
Carefully pour the batter over the banana slices in the pan, smoothing lightly with a spatula as needed. Bake for 42 to 45 minutes or until the cake is set in the center and a toothpick inserted comes out clean or with a few moist crumbs. Allow the pan to cool on a wire rack for at least 3 hours before inverting and serving.
05 -
If you lined the pan with foil, lift the cake out using the foil overhang. Place a cutting board on top, invert, and gently remove the foil to reveal the topping. Slice and serve.