Place peanut butter in the bottom of blender (this helps make sure it's fully incorporated)
Add bananas
Blend on high for several minutes
Scrape down sides & continue blending until creamy
Transfer to medium size bowl & fold in jelly/jam being careful to not fully blend it in. You want ribbons of jelly throughout.
Enjoy immediately for a soft serve ice cream or transfer to air tight container & freeze overnight for firm ice cream.