what to do with your rollmop thanks to Hugh F-W

Herring, potato and watercress salad
This makes a delicious, punchy main-course salad; leftovers are good in a lunchbox the next day. Serves four to six.
400g small, waxy potatoes300g rollmop herring (see previous recipe)1 small shallot, peeled, halved and finely sliced1 tbsp dill fronds, chopped1 big handful watercress
For the dressing½ tbsp wholegrain mustard1 tsp freshly grated (or prepared) strong horseradish½ tsp dry mustard1 tbsp cider vinegar3 tbsp olive or rapeseed oil, plus ½ tsp extra for the watercressA good pinch of sugarSalt and freshly ground black pepper
Whisk together the ingredients for the dressing. Taste and add a little more sugar if necessary.
Boil the potatoes until tender. Drain and, when cooled just enough to handle, halve and toss in the dressing. Set aside to cool.
Cut the rollmops into bite-sized pieces and mix gently with the ­potatoes, shallot and dill. Dress the watercress with oil, turning it with your hands, and season. Divide the salad between four plates and spoon the potatoes and herring on top.