Open cans of sweetened condensed milk and pour into three half pint jars, dividing evenly. Put on lids and rings.
Place jars in crock pot and add water to just reach the bands of the jars.
Cook on low heat for 6-8 hours (for caramel sauce consistency) or 10 hours (for a consistency more like pudding; see notes).
Carefully, remove jars from the crock pot and enjoy!