Pick the leaves off some sorrel that has been growing in the sun.
Sorrel looks similar to another plant called Japanese dock, so keep that in mind. In this photo, the Japanese dock leaf is on the top, with the sorrel leaf below. (Japanese dock is edible as well.)
Mince up the sorrel leaves. (This can be done roughly, and it's also possible to make the jam without chopping them at all.)
Add the minced sorrel leaves to a saucepan with the sugar and a small amount of water and simmer it down.
The resulting jam may look a little dangerous but it's fine! It has a delicious bittersweet flavor.
Story Behind this Recipe
I remember finding sorrel to be too sour as a kid. I heard that it's used in a lot of French cooking so I tried making some jam. I've tried a lot of other recipes too, you can check them out here.
I picked these sorrel leaves at the beginning of spring, so the jam is quite black. If you pick the leaves in winter I heard that you'll get a red-colored jam. If you're worried about the poisonous-looking colour, try picking the leaves in winter.