Preheat the oven to 350°F. Line cookie sheet with parchment.
Combine the soft butter and sugar in your mixer bowl. Beat on medium speed for 2 minutes. Beat in the egg and vanilla.
In a small separate bowl, whisk together the baking soda, salt, baking powder, cocoa, and flour. Add to the wet ingredients and mix on low speed until well combined.
Allow the dough to sit for a minute while you make the fudge topping. In a microwave-safe bowl, heat the chocolate chips and condensed milk for 30 seconds. Stir. Heat for additional 10 second intervals if needed. Stir until smooth. Avoid over heating or the topping will dry out.
Scoop the dough into 24 balls, I used my small cookie scoop. Place the balls on the prepared baking sheets. Use your thumb to press an indentation into the center of each ball, then widen it to make a small cookie dough "nest."
Place a banana slice into the "nest" in each cookie. Cover with two teaspoons fudge topping. You can roll the topping into a ball and flatten with your finger to get a thin layer of fudge to cover the top of the cookie.
Bake the cookies for 10 to 12 minutes. Transfer to a cooling rack. Serve and enjoy.