Preheat your oven to 325 degrees F. Spray three 8-inch pans or four 6-inch pans with nonstick spray, line the bottom with parchment paper and spray again. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and the sugars on medium-high speed until light and fluffy, about 2 minutes.
Gradually add the eggs, scraping the sides of the bowl with each addition, Mix for about 2 minutes on medium speed after all the eggs are added.
Add the mashed bananas and vanilla. Stir until combined.
In a medium sized mixing bowl, whisk the flour, cocoa, baking powder, baking soda and salt.
In a small mixing bowl, combine the buttermilk and sour cream. Whisk to combine.
With the stand mixer on low speed, alternately add the the flour mixture and the buttermilk mixture, starting and ending with the flour. Mix just until the ingredients are combined.
Stir in chocolate chips by hand.
Divide the batter between the three 8-inch pans (about 20 ounces in each), and bake for about 30 to 33 minutes, or until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it.
Let the cakes cool in the pans for 15 minutes and then invert onto wire cooling rack to cool completely.
Cake layers can be made ahead of time and wrapped in plastic wrap and stored in the freezer. Allow the cake layers to thaw for about 30 minutes before you stack and decorate the cake.
I do NOT recommend using bake even strips on my cakes.