I have a thermos vacuum pot, and do stews and soups with it once a week where I just bring things to a boil and leave it in the insulated thing overnight.

Oxtail soup, pork spareribs, chili, biryani, hunter's stew, etc. Helps it with getting everything really nice and tender, and easier than a slowcooker.

It’s how pit barbecues work as well. You heat rocks on a fire and then bury the food (like a lamb) with the rocks under the ground, using the dirt as an insulator.

Or, cover the rocks and food (like lobster or oysters) with wet seaweed to steam the food.

Also yoghurts have been made using a jar in some insulated slow cool down method for centuries

I have a "Wonderbag," an insulated bag you put your pot in after bringing it to temperature. It does keep heat in for a very long time.

> a pot roast brought to a boil in the morning, then put in a well insulated container to sit for the day.

Don't you need to worry about some sort of danger zone with regards to bacteria in meat thriving between 100-140F? My friend always leaves meat out for several hours and never gets sick, but I've just assumed he's been lucky so far.

I’d assume if the lid was kept on then there’s little scope for new bacteria to enter the chamber

> it was something like a pot roast brought to a boil in the morning, then put in a well insulated container to sit for the day.

https://en.wikipedia.org/wiki/Haybox: “A haybox, straw box, fireless cooker, insulation cooker, wonder oven, self-cooking apparatus, norwegian cooker or retained-heat cooker is a cooker that utilizes the heat of the food being cooked to complete the cooking process. Food items to be cooked are heated to boiling point, and then insulated. Over a period of time, the food items cook by the heat captured in the insulated container. Generally, it takes three times the normal cooking time to cook food in a haybox.”