Preheat the oven to 200C/Gas 6/fan oven 180C. Roughly prick the potatoes all over with a fork and bake in the oven for about 1 hour or until tender.
Remove from the oven, leave until cool enough to handle, then cut each potato into eight wedges and put in a large bowl with the olive oil. Season generously. Mix well, making sure that each wedge is well coated with oil and seasoning.
Stand the potato wedges on a large non-stick baking sheet and roast in the oven for 20-30 minutes or until really crispy and golden. Meanwhile, mix the soured cream in a serving bowl with the horseradish and snipped chives.
Serve the wedges straight from the oven, with the soured cream for dipping.
Prepare ahead: bake the potatoes and make and chill the dip the day before. Two hours before your party, prepare the potatoes from step 2 and put in the oven half an hour before your guests arrive.
Stagger the cooking: roast in two batches – half before the party starts and half when these have been eaten.