In a small mixing bowl, whisk together 2 tsp sugar (omit if the herring has been marinated in sugar), 1 tbsp cider vinegar, 1 tbsp wholegrain mustard, 1 tsp Dijon mustard, and 2 tbsp crème fraiche. Slowly whisk in 50 ml rapeseed oil to form an emulsion. Fold in 1 small shallot finely chopped and a handful of chopped chives.

Fold some of the dressing into a bowl of warm, boiled waxy new potatoes (peeled and cut into bite-sized pieces). Fold in slices of pickled herring* to taste. Sprinkle with additional chopped chives.

Extra sauce will keep nicely for a few days in the fridge.

* I like Orkney herring (fished between the Orkney Islands and Scandinavia).