Growing up in New Hampshire, we had a soft-serve ice cream shop named King Kone. King Kone had never more than six flavors: usually chocolate, vanilla, twist, banana, black raspberry, and bananaberry. Their soft serve was excellent and the cones were huge, and if you ever visit Merrimack, NH in the summer, be sure to check it out.
This recipe doesn't really have anything to do with commercial soft serve, but it sure is good. And healthy!
Take three bananas (overripe or ripe) and cut them into pieces, then freeze. To make the ice cream, take the bananas out of the freezer and let them soften for a minute or two.
Put the banana pieces in a food processor and blend until the ice cream is light and airy. It will take about 2-3 minutes; scrape down the bananas as needed.
The boys love this - the first time I made it, I told them they were having ice cream for breakfast. It's amazing how creamy, rich, and smooth the bananas become, truly mimicking the texture and flavor of soft serve.