Classic new potato salad

Method

1. For the mayonnaise, put the egg yolk, ¼ tsp salt, mustard and vinegar into a small bowl and mix together lightly. Very gradually trickle in the oils, beating continuously with a hand-held electric mixer, until you have a smooth, thick emulsion. Season with freshly ground white pepper.
2. Put the potatoes in a pan of well salted water (1 tsp per 600ml), bring to the boil and simmer for 12-15 minutes or until just tender (cooking times will vary according to the freshness, size and variety of your new potatoes). Meanwhile, mix 2 tsp of the vinegar and the mustard together in another small bowl and gradually whisk in the oil to make a smooth, thick vinaigrette. Season to taste and set aside.
3. Drain the potatoes, spread them out on a tray and leave to cool slightly, then cut each one into 2 or 3 chunky pieces. Transfer to a large mixing bowl and gently stir in the dressing, taking care not to break up the potatoes. Leave to cool completely, during which time they will absorb all the dressing. Meanwhile, chop the spring onions, pickled cucumbers and boiled eggs.
4.  Put 6 tbsp mayonnaise and the soured cream or crème fraîche into a bowl, then mix in the remaining vinegar, ¼ tsp salt and some white pepper. Stir this into the cold potatoes with the spring onions, pickled cucumbers, parsley, three-quarters of the chopped dill and three-quarters of the chopped hard-boiled eggs. Transfer to a clean serving bowl and sprinkle with the remaining egg and dill. Serve at room temperature.