Using an electric handheld or stand mixer, beat the butter and sugar together in a large bowl until light and fluffy.
1 cup unsalted butter, 1 cup sugar
Add the vanilla and eggs, one at a time, mixing in between.
1 tsp vanilla, 2 large eggs
Add half of the flour mixture, beat on low speed, then add the sour cream and bananas, mix again.
1/2 cup sour cream, 2 cups mashed overripe bananas
Add the remaining flour mixture, beat until just combined and stir in chocolate chips.
1 cup mini chocolate chips
Divide the batter among the 2 prepared pans. Bake for 40 minutes or until the cakes are golden brown and pull away from the edges. Let cool completely and chill in refrigerator until ready to frost.
To make the buttercream:
Melt the chocolate in a double boiler and let cool to touch.
1 pound milk chocolate chips
Beat together butter, sugar and salt until pale and fluffy. Slowly beat in melted chocolate, then sour cream, and beat until smooth. Frosting can simply be spread on top and around the cake or piped on, if you want to get fancy.