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Preheat oven to 350 degrees F. Grease three 9-inch cake pans; generously dust with flour.
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In a large bowl whisk together flour, baking powder, baking soda, salt, and cinnamon; set aside.
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In a large bowl cream together the butter and sugars with an electric mixer on medium speed for 3-5 minutes or until light and fluffy. Add in vanilla and eggs; mix until well combined.
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Turn the mixer to low speed and add in the mashed banana until well incorporated.
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Add in half of the flour mixture, sour cream, and buttermilk; mix until just combined then add in the remaining flour and beat again until just combined. Do not overmix! Using a wooden spoon or rubber spatula, gently fold in chocolate chips.
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Evenly pour batter into cake pans. Bake for 20-25 minutes or until tester comes out with a few crumbs attached.
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Cool cakes for 10 minutes on wire racks then invert and turn cakes onto racks to finish cooling completely.
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To make frosting: In a large bowl, beat butter and peanut butter until light, fluffy and smooth. Slowly add in confectioner’s sugar and milk. Add in additional milk if needed and depending how thick you like your frosting.
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Place 1 cake layer on stand. Spread a heaping cup of frosting over the top. Add some sliced bananas if desired. Place another layered cake on top. Repeat until you get to the last layer.
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Spread remaining frosting over the top and sides of cake. Cover cake and chill. Let cake sit out an hour or two before serving.