Line a baking sheet or tray with parchment paper. Slice bananas and place on the prepared tray. Cover with plastic wrap. Transfer to the freezer and freeze until solid, at least 2 hours.
Have all the ingredients measured and equipment ready to go before you remove the bananas from the freezer. Place bananas, peanut butter powder, cocoa powder, and milk in the bowl of a food processor fitted with the blade attachment or the bowl of a blender. Process until smooth and creamy. Serve immediately or transfer to vessel to store and freeze for later