Jam, in my opinion, is mostly a way to divest of Ball jars, which are a commodity these days. Beginning canners make a lot of jam, and I always wonder who is eating it all. But I stand behind a green tomato jam. It is a delightful culinary surprise that earns its spot on a cheese plate, but what I like most about it is the simplicity.
A word of caution to jam noobs: Jam is a “fuck around and find out” culinary experiment. Do not change the ratios. Do not double the recipe. If you want your jam to gel, you gotta play by the rules of engagement. You want 1 pound sugar + 3 ¼ pounds of tomato + 1 medium lemon. Yes, one pound of sugar. Get over it. You’ll have to, because if you short it, you won’t have jam. We’re also looking for 3 1/4 pounds of tomatoes after you remove your black spots, stems, cores, etc. Halve them, remove the seeds, rough chop and toss with the sugar and lemon in a ceramic or glass bowl and leave them overnight, covered, in your fridge.
The next day, low boil the mixture for 75 minutes, immersion blend, then pour into jars. You can refrigerate your jam immediately to eat within a few weeks, or, if you’re using wide mouth jars rated for the freezer, freeze them. You can also go the whole mile and process them to be shelf stable, following all the recommended guidelines for canning at your altitude. I enjoy a half pint jar for this use, which you process at the same times for a pint.