Place frozen banana slices and cocoa powder, I used 1 ½ tablespoons for a mild chocolate flavor (can add more for richer chocolate flavor), into a food processor or high-speed blender. Blend on high for 1 minute, stopping to scrape the sides.
Bananas will start off looking crumbly. Continue to blend, stopping to scrape down the sides every so often. Add a tablespoon of milk, process and scrape down the sides. The clumps should start to bind together to form a gooey mixture.
Add another tablespoon of milk to get it to the perfect creamy consistency. The nice cream should look similar to soft serve ice-cream texture at this point. *
Add the peanut butter, pulse 3-4 times. Then add the peanut butter cups and either stir in or pulse 2 times.
Scoop the nice cream into bowls and enjoy right away with your favorite toppings. If you prefer a firmer texture, place in a container, and into the freezer for 30 minutes to 1 hour.
If you freeze the nice cream for longer, it will become solid and hard to scoop. Thaw on the kitchen counter for 10-15 minutes before serving. Be sure to store in an airtight container to prevent freezer burn.