Boil up 500g baby new potatoes (or Jersey royals, if in season), till just tender.

Meanwhile, in a bowl, whisk together 2 tbsp cider vinegar, 2 tbsp Dijon mustard, 2 tbsp whole-grain mustard, 2 tbsp finely chopped dill pickle, 1 tbsp pickle brine, 2 tbsp finely chopped dill, 1 tsp sugar, and a pinch of freshly ground pepper.

Drain the potatoes, cut in half, and then place in a salad bowl. Add ¾ of the mustard sauce (while the potatoes are still warm) and stir till well-coated. , 

Add two large handfuls of watercress (pea shoots make a nice alternative) and mix to coat. 

Add a drizzle of olive oil, season with salt,  and top with more fresh dill.

Serve with Smørrebrød (Scandinavian open-faced sandwiches).