In the old days, they were called Hay Boxes. Before leaving the house to work in the fields, people would place the ingredients for lunch in a pot pre cook, then place in a box covered with hay and blankets to keep it cooking and warm for when they returned. The original slow cooker.
Nowadays, there are a lot of slow cookers on the market. But You can make your own custom cooker and yogurt maker. No electricity required!
At Airesbuenos we made one to prepare delicious meals and yogurt. You can make one yourself for very little investment. All you need is
A box with a lid
A pot that fits completely inside the box
A tube of expandable foam
Wait, you can make yogurt too!