Step 1

Tip the potatoes into a large pan of cold salted water. Bring to the boil, then simmer for 10 mins until tender to the tip of a knife.

Step 2

While the potatoes are cooking, whisk the mustard, vinegar, olive oil and chopped shallot together with a good pinch of salt and a grind of pepper. When the potatoes are cool enough to handle, peel if you prefer, then halve, quarter or cut them into bite-sized chunks if large, then toss in the mustard dressing until completely coated. Leave to cool completely.

Step 3

Meanwhile, mix the mayonnaise, soured cream, lemon juice and horseradish together. When the potatoes are cool, toss them through the mayonnaise mixture along with the spring onions. Tip into a dish and scatter with the crispy onions just before serving, or serve the crispy onions on the side for sprinkling over at the table.