Preheat your oven to 200 degrees F. Place your canning jars, lids and rings on a sheet pan in the oven to sterilize while you make your jam.
Place all of the ingredients in a large pot over the stove.
Bring the pot to a boil, then immediately turn down the heat and simmer for 10-15 minutes, or until bananas soften up.
Use your immersion blender or a potato masher to mash the bananas to a smooth puree.
Carefully remove the jars, lids and rings from the oven. Ladle your banana jam into the jars. Quickly apply the lid and ring and tighten, finger-tip tight.
As the jars cool, the heat within the jar will pull the lid downwards to create a seal (jars will ping).
Store in a cool pantry. Since these jars are not canned for long term storage, I would recommmend consuming within 30 days.