Preheat the oven to 350°F. Butter and flour a standard bundt pan. Set aside.
In the bowl of a stand mixer cream together the softened butter, peanut butter, granulated sugar, brown sugar and vanilla. Beat for 2 minutes or until creamy and fluffy.
Add the eggs one at a time beating well after each addition.
On low speed, add the flour alternately with the buttermilk. Stop and scrape the sides of the bowl as needed.
After all is added increase the speed of the mixer and beat for 1 minute or just until combined.
Mix-in the mashed bananas and mini chocolate chips by hand.
Spread evenly into the bundt pan, bouncing the pan on the counter a couple of times to release air bubbles.
Bake for 1 hour or until a cake tester inserted into the center shows moist crumbs. Cool in the pan on a baking rack for 1 hour then remove from the pan and cool completely.