Boil the potatoes, ideally with the skins on, in a large pan of well-salted water for about 6 minutes.Then take the pan off the heat and leave the potatoes to stand in the cooking water with the lid on for about 15 minutes (depending on size). This gives them a lovely firm texture and ensures the potatoes don't fall apart. Test with a skewer that the potatoes are tender before draining – otherwise leave them to stand a little longer.
Peel the potatoes, leave them to cool, then cut them into bite-sized pieces.
Slice the cucumbers. I prefer to use mini cucumbers. They have a good thickness and are wonderfully crisp.If your cucumbers are very thick, I recommend removing the seedy centre and then cutting the cucumber into chunky pieces.
Cut the onion into quarters, then into "strips".
Mix the ingredients for the dressing and season to taste with salt and freshly ground pepper.
Put the potatoes, cucumber, red onion and dressing in a bowl and toss well to combine.If you can, leave the potato salad to stand for a little while before serving.