Preheat your oven to 425 degrees F. Line a baking sheet with parchment paper. Set aside.
In the bowl of an electric mixer, fitted with the paddle attachment, combine the butter, peanut butter, brown sugar, and vanilla. Beat on medium speed until light and fluffy, about two minutes.
Add the egg and egg yolk beat until just combined.
Stir in the banana.
Add the flour, baking powder, baking soda and salt and mix on low speed until just combined.
Stir in the peanut butter chips and chocolate chips.
Using a cookie scoop (mine is about 2 tablespoons and made 2.5 oz. size cookies), drop cookie dough on lined baking sheet about 2 inches apart. Do not flatten these cookies. Sprinkle a little sanding sugar and chopped peanuts on top of each cookie.
Bake for 6 to 8 minutes, or until golden brown on top. Allow to cool completely before eating.
Makes about 16 large cookies.