The Nottingham jar is a large, earthenware pot with handles and a lid – a little like a crick pot, I guess. I’m sure it does exactly the same as a modern slow-cooker, but somehow I also imagine something slow-cooked in a Nottingham jar in the oven would be taste better. I’ve seen nineteenth century adverts from them sized from a pint to four quarts – that’s a gallon! They were sold with or without lids but I can’t quite think why you would want one without a cover.
Here is a recipe from 1920:
An easy way to pickle plums is to remove stalks, discard all bruised and overripe; plums; wipe sound plums with a cloth and arrange them in layers in a Nottingham jar, .with .a liberal allowance of good brown sugar sprinkled be tween. Fill up the jars with cold vinegar, tie them down, and bake, in a rather slow oven till the plums are tender, then tie down. Any spice such as stick cinnamon and allspice berries with mace, may be added according, to inclination.