Here's the recipe from my plum ketchup experiment the other day. It's not quite got the HP sauce taste I was aiming for, maybe due to the lack of dried fruit compared to the Cherry Plum Chutney recipe, but it is a lovely, tangy, tingly on the tongue sauce and such a beautiful colour too.
Norfolk Kitchen Cherry Plum Ketchup.
2 kilos cherry plums
2 onions chopped
440ml vinegar (any kind except malt)
30g ground ginger
1tsp cayenne pepper
Generous pinch mixed spice
Stone the plums, add them to a pan with all the other ingredients. Bring to the boil and simmer for about 40 minutes until the mixture is thick and jammy. Briefly blend everything together (I used a stick blender) then push through a sieve into a clean pan. Taste and adjust seasoning if needed. Makes approx 2 litres.
I'm not sure how long this will keep though I suspect it's not long as it's fairly light on the vinegar and sugar. To get around this I've got one bottle in the fridge and have put the excess into plastic bottles and stored them in the freezer.
The main advantage of home made ketchups versus shop bought, in my opinion, is their natural non-plasticy taste which gives them greater versatility. They're perfectly acceptable poured over most things I would never introduce to Heinz, like Pizza, omlettes or cheese on toast.
Right then, next on the experiment list: Yellow Bullace and ginger cordial.