Remove the frozen banana slices from the freezer and let them sit at room temperature for 2-3 minutes to soften slightly.
Add the frozen bananas, milk, vanilla extract, and peanut butter to a high-powered blender or food processor.
Blend on high speed, stopping frequently to scrape down the sides and break up any chunks, until the mixture is completely smooth and creamy like soft-serve ice cream, about 2-3 minutes total.
Stir in the chocolate chips by hand, then serve immediately for a soft-serve consistency, or transfer to a freezer-safe container and freeze for 1-2 hours for a firmer texture.