Cut bananas into 1 inch thick slices. Place on a freezer safe tray or plate and freeze until firm, at least 2 hours.
Add the frozen bananas into the bowl of a food processor and process until completely smooth. This takes a few minutes and you may need to scrape down the bowl or break up large chunks.
Once the banana is creamy, add the peanut butter and vanilla and process until combined. Eat immediately for a soft serve like treat or place in a freezer safe container and freeze until firm or up to 1 day.