Peppered mackerel and potato salad with mustard dressing

My husband seems to have taken over in the kitchen recently which isn't too good for this blog so I'm having to raid the back catalogue for recipes. This is another that went into the giveaway Guardian student book I wrote for them a couple of months ago. I'm not mad about smoked mackerel but it's fantastically good value and works brilliantly in this chunky potato salad

Serves 3-4
45 mins including cooling time

450-500g new potatoes
1/2 a small onion, peeled and finely chopped
2 level tsp Dijon mustard
2 tbsp wine or cider vinegar
6 tbsp light olive oil or sunflower oil
200g peppered smoked mackerel
A handful of chopped parsley or some snipped chives (optional but adds a bit of colour)
Salt and pepper

Wash and scrub the potatoes clean leaving on the skins. Cook in boiling salted water until just tender (about 12-15 minutes) then drain and leave until cool enough to handle (another 10 minutes or so). Meanwhile whisk together the mustard and vinegar in a bowl and season with salt and pepper then gradually whisk in the oil plus a tablespoon of water if it seems a bit thick. Slice the potatoes roughly into the dressing and leave for another 15 minutes if you’ve time for the flavours to absorb. Pull the mackerel off the skin and break up with a fork into largeish pieces, removing any bones and lightly mix with the potatoes and parsley. Serve straight away (potato salads are never as good if they’re chilled)

IMO you can never have too many potato salad recipes. What's your favourite?