Place the damsons in a large preserving pan and cook them for about 10 minutes with 100ml water, until they are soft and the stones popping out.
The easiest way to remove the stones is to strain the damsons, spread the pulp out on a large plate then pick through all the pulp carefully with food grade gloves to remove each stone. Place the de-stoned pulp and the damson juice back into the preserving pan.
Add all the rest of the ingredients and bring to a boil. Turn the heat down and simmer for 30 minutes.
Pour everything into a blender and blitz until smooth.
Pour the sauce back into the preserving pan, taste for seasoning and bring back to a gentle boil.
Remove from the heat and decant into sterilised jars.
Inspired by Liana Krissoff's Chinese Plum Sauce from Canning For A New Generation