Place tomatoes in a food processor and process into small chunks.
In a saucepan, over medium-low heat, carmelize the onion in the butter until light brown, about 20 minutes. Add the tomatoes and the remaining ingredients and simmer for 1½ to 2 hours, stirring periodically, until the jam has reduced by about half and is thick, like a very thick tomato sauce.
It will keep for 2-3 weeks in the fridge.
Recipe by Healing and Eating at https://www.healingandeating.com/2015/03/tomato-jam-make-it-paleo-ii-review-giveaway.html