Here's a good article (with pictures) of a slow simmering soup that has a long history. The author calls it a "pioneer dish" hearkening back to the Old American West but I think you could have probably found pots of this around ancient Roman soldier's campfires too.
While the article talks about cooking this dish in a Dutch Oven and over a open fire, for a world of less energy a Green Wizard would probably use a solar cooker and a haybox. Now that I have time, I plan on getting more regimented with my cooking. Having something like this soup simmering over the weekend seems like a great idea, especially with the coming Winter.