I just saw this suggestion recently and tried it a few days ago and it worked! Banana "ice cream". No other ingredients needed, just banana. But it can pass for ice cream. There are some variations out there (things you can add), so I did one of those. Here's what I did:
Had three overripe bananas. Peeled and sliced, put on a baking sheet and threw in the freezer for an hour or so. Took out semi-frozen and put into the cup for my immersion blender (recipes say to use food processor, but the immersion blender did just fine for me). Blended a minute or two until smooth (soft-serve/soupy consistency). Since I had some Nutella around and that was a variation I'd seen, I put in 1/3 cup (or so) of that. Blended just a bit more. Dumped into a Pyrex container and put in the freezer overnight. And it really did turn out just like traditional ice cream (banana hazelnut chocolate flavored). We are still enjoying it!
I will definitely do this again, as it was quick and easy and way cheaper than buying ice cream!