Mackerel salad with Georgian-style plum sauce

Bring a kettle of water to the boil. For the plum sauce, score the base of each plum with a cross, then put in a heatproof bowl and cover with boiling water. Leave for 2-3 minutes, then drain, rinse under cold water and pull off the skins. Roughly chop the flesh and put in a small saucepan with the remaining sauce ingredients, apart from the salt and dill. Add 75ml water, bring to a simmer and cook for 10 minutes, covered, until the fruit is really soft. Using a stick blender, whizz the mixture until smooth, then stir in the dill, salt and some ground black pepper. Cook for another 5 minutes, uncovered, to thicken slightly, then taste: depending on the plums, it may need some more vinegar or sugar. Set aside to cool. (You can serve this warm or at room temperature, but it’s best not piping hot.)

Put the lamb’s lettuce, mackerel and plum wedges in a large bowl with ½ of the dill and ½ of the walnuts. Pour over the sauce (you may not need it all). Serve topped with the remaining dill and walnuts, plus lemon wedges.