Preheat oven to 350°F. Line a cupcake pan with paper liners and set aside.
In a large bowl, mix together flour, baking powder, baking soda and salt.
In another bowl, add butter and sugar and beat with an electric mixer on medium until blended. Add sour cream and vanilla and continue beating. Add the egg and egg yolk and beat after each addition.
Combine the wet ingredients with the dry ingredients and mix together until blended.
Fold in bananas and chocolate chips.
Fill each cupcake about ¾ of the way full with an ice cream scoop. Bake for 20 to 25 minutes, or until a toothpick comes out clean.
Let cool for 10 minutes before removing them to a wire rack. Cool before frosting.
To make the frosting, beat the butter and peanut butter with an electric mixer on medium until smooth. Add in icing sugar slowly and continue to beat. Add in milk and beat until smooth.
Place icing in a pastry bag with a large tip and frost the cupcakes. Garnish with chocolate chips, if desired.