Preheat oven to 350 degrees F. Lightly grease two 9-inch round cake pans with baking spray and set them aside.
In the bowl of a stand mixer fitted with a paddle attachment, combine the eggs, oil, buttermilk, and vanilla extract. Mix on medium-low until everything is nicely blended.
With the mixer on low, gradually add the dry ingredients to the wet mixture. Pause occasionally to scrape down the sides of the bowl and ensure everything is mixed thoroughly.
Once the batter is mostly combined, fold in the mashed bananas and mix just until everything is smooth.
Evenly pour the batter into the prepared pans and place them in the oven.
Bake for about 30 minutes, or until a toothpick inserted in the center of the cakes comes out clean.
Let the cakes cool in their pans for about 10 minutes, then gently turn them out onto wire racks to finish cooling completely.
Filling
Clean and dry your mixer bowl. Then, beat the cream cheese together with the instant pudding mix on low speed until the mixture is smooth. Scrape the bowl as needed.
Slowly pour in the heavy cream while mixing, then increase the speed to medium. Beat until the mixture becomes thick and fluffy—this should take about 3 minutes.
Once the cakes are completely cool, place one layer on your serving platter. Spread the pudding mixture evenly over the top.
Layer thinly sliced bananas over the pudding for added texture and flavor.
Frosting
Rinse and dry the mixer bowl again. Add the softened butter and beat it on medium speed until it’s light and creamy.
Next, add the whipped topping and continue mixing until fully combined.
Gradually sift in the powdered sugar, mixing until the frosting is smooth and spreadable. Scrape down the bowl occasionally for an even texture.
Once the filling is set, frost the top and sides of the cake with the whipped buttercream mixture.
(Optional) For a beautiful finishing touch, decorate the cake with banana slices, vanilla wafers (whole or crushed), and fresh mint leaves if you like.
Notes
For the mashed bananas, use very overripe bananas, but not black.
Use ripe but firm bananas without too many brown spots for the sliced bananas in the filling and garnish.
For the bananas used for garnish, brush them with a bit of lemon juice to prevent them from turning brown.
The cake is fine without any garnish, but if serving guests, you can make it pretty with crushed vanilla wafers, whole vanilla wafers, or a combination. Sliced bananas look lovely as well.
Storage: Cover cake tightly and store in the refrigerator for up to 5 days. Remove 15-20 minutes before serving, then return to the refrigerator. This cake does not freeze well due to the different layers.