1) Put the potatoes into a large saucepan and add the stock and enough water to cover to a depth of 2.5cm. Bring to the boil and cook the potatoes for 12 to 15 minutes until tender. Drain the potatoes and place back in the hot pot.
2) Combine the spring onions, celery, vinegar, sugar, horseradish and olive oil in a small bowl. Pour the dressing over the hot potatoes and leave to absorb.
3) Season the salad with dill, salt and pepper and celery seed, if desired.