Wild plums are too tart and acidic for eating raw but these qualities make them ideal for jams and sauces. Think of this sauce as being akin to a Chinese plum sauce - sweetly spiced and fruity. It is made in two stages to allow the opportunity to test its sweetness and gauge how much to reduce the sauce.
It is served here with some simply cooked fresh mackerel, but would also be lovely as a dipping sauce for deep-fried prawns, ribs, or duck.
For the spiced wild plum sauce:
300g wild plums
100g sweet purple plums, halved
1 cinnamon stick
2 star anise
11/2 tsp yellow mustard seeds
1/2red chilli, chopped
2 tbsp soft brown sugar
75ml red wine vinegar
1/2tsp freshly grated ginger
Keep the wild plums whole and put them into a pan with the sweet plum halves and their stones. Add the cinnamon stick, star anise, mustard seeds and chopped chilli and stir over a low heat for a minute to get the fruits and spices going. Add the brown sugar, stir for a few seconds, then add 125ml water and a good pinch of salt. Next stir in the vinegar and the ginger.
Increase the heat and simmer for 15 mins. Strain the contents of the pan into a large bowl, really pushing at the fruits to get everything out. Return everything to the pan - the pressed out liquid, what is left behind in the sieve and what has been caught on the underneath of the sieve. Stir, taste, and add more sugar, salt or spices as you prefer. Simmer again for 5 mins or until you achieve the thickness of sauce you want - a dipping sauce would need to be thicker (so reduced for longer) than the pouring sauce used here.
Strain, again pushing to get as much as possible through the sieve. Use the wild plum sauce immediately or keep it in the fridge for up to a week.
For the mackerel:
8 fresh mackerel fillets (or 4 whole mackerel, butterflied and de-boned)
Melt half the butter in a large frying pan. Once it is sizzling lay 4 of the mackerel fillets (or 2 of the butterflied whole ones) skin-side down. Season the flesh side, and allow to cook for 3-4 mins. Once the flesh has turned completely white (from being translucent) turn them over and cook for another minute. Remove from the pan and keep warm while you do the second batch. Serve with the spiced wild plum sauce.
(This recipe originally featured for Borough Market.)