Mince the herbs finely, or pulverize them in a spice grinder. Melt the butter in a pan large enough to hold all the ingredients (for large batches, perhaps a roasting pan). Turn the heat down to low and stir in the herbs and chilies. Chop the onions into slices about a third of an inch wide and no more than a couple of inches long. Add to the pan along with the salt, and stir to coat onion slices with butter. Cook over medium heat, stirring occasionally, until onions are soft and brown, an hour or more.

In the meantime, prep the tomatoes. For cherry tomatoes, just slice them in half. Larger tomatoes should be peeled and cut into chunks no larger than an inch. When the onions have caramelized, add the tomatoes, vinegar,and sugar. Cook until it's thick and somewhat jammy, an hour or two. Keep in mind that it will be a much thicker consistency when cool than when it’s bubbling on the stove.

Preserves: The jam will keep for several weeks in the fridge, or can be preserved by pressure canning or by freezing.