4tablespoonButter unsalted½ stick room temperature
½cupUnsweetened cocoa powder42 g
¼cupCrisco shorteningroom temperature
Mash 2 bananas in a bowl and set aside. Weigh or measure both sugars into a dish and set that aside. Weigh or measure the flour, baking powder, baking soda, and salt into a bowl, running a whisk through to blend.
On your stove, add the butter to a saucepan and heat over medium heat stirring the whole time. It will go in stages; first, it will look like a white film on top. Next, the butter will start to get a little clear, and you will begin to get transparent bubbles. Be careful; this is the stage that it can go too far very quickly. The butter should be a dark golden brown and have a nutty smell if you lean over the pan. Take it off the heat. If you end up with a lot of dark brown specks at the bottom of the saucepan, it will have a burnt taste. Add both sugars to the brown butter and stir till all the butter is incorporated into the sugars. Let it cool for about 10 minutes.
In a stand or handheld mixer, add the cooled butter-sugar mixture and turn the mixer on medium-low speed. Add the vanilla extract, bananas, egg, and sour cream and blend. Turn the mixer to low and slowly add the flour mixture till incorporated. I scrape down the sides and across the bottom and finish mixing for another 30 seconds. The cookie dough will be soft, so I take the bowl off the mixer and fold in the chopped walnuts. Cover loosely and refrigerate for 30-60 minutes.
Preheat the oven to 350° and line 2 cookie pans with parchment paper. Taking a small cookie scoop, place 12 scoops onto a pan. The dough is a little sticky, so I get e small dish of water and a paper towel and wet two fingers and gently press down on each top of the scoops. You don't want your fingers so wet that it forms puddles on the top of each cookie, and you can dab it with the paper towel gently if it is too much. I just wet my fingers, so they do not stick to the cookie dough. Bake for 9-11 minutes and move to a cooling rack once the pan comes out of the oven.
ICING FOR THE MIDDLE
Weigh or measure the powder sugar, cocoa powder and run a whisk through to blend. In a stand or handheld mixer, add the butter and Crisco shortening and combine. You need both of them room temperature, or they will clump and not mix. Turn the mixer down to low speed and gradually add the powdered sugar and cocoa mixture. Go slow, or you will end up with it spraying all over your counter. It will be thick, so add 4 tablespoon of milk to start with and increase if you need it thinner for the icing to go through a piping bag.
You can use a knife to spread the icing over the bottom of a cookie or a piping bag if this is what you prefer. I used a piping bag and a Wilton #10 tip, but you can certainly use what were you have on hand that will fill up the center of the cookie. Take one of the other cookies and put it on top of the icing, and you have a cookie sandwich with the icing in the middle.