This probably belongs in the old news category, because this trick has been bouncing around the internet for a few years, but I finally tried making ice cream from frozen bananas and was amazed by how good the outcome was. I first read about this technique on The Kitchn a couple of years ago; this post describes how you can use a single ingredient to make delicious ice cream.
One of the most challenging parts for me was accumulating enough overripe bananas to conduct the experiment--we go through bananas very quickly and never make it to the end of the week with extra bananas. I finally decided to buy double the normal amount so that I could freeze a few fully ripened bananas. Once you have some nicely brown-speckled bananas, peel them and break them into chunks (or slice them), and freeze them in a ziplock bag. Let them freeze for a few hours (or a few days or weeks). When you're ready to make some ice cream, take the bananas out of the freezer and let them sit at room temperature for 10 minutes.
I didn't believe it until I tasted it myself, but this stuff really does taste like excellent ice cream. The texture blew me away, and it's got a delicious pure banana flavor. Best of all, I can feed my kids a banana for dessert and they think they are getting a very special treat.