Slice the bananas into 1-inch-thick coins and freeze them on a parchment-lined cookie sheet for about an hour. Then, put the frozen banana coins, cocoa powder, and vanilla extract in a food processor and process till smooth. If you don't have a food processor, you can use a high-speed blender. Add milk in tablespoon increments to help in the blending process.
Pour into a loaf pan or freezer-safe dish and freeze for 3-4 hours. Scoop out just like regular ice cream, and enjoy!
Notes
The riper the bananas, the sweeter the nice cream will be.
Add-ins: Add chocolate chips or nuts on top of the nice cream or after processing it for flavor variations or crunch.