2) While the potatoes are cooking and cooling, fry the bacon in a large nonstick frying pan, then remove to a paper towel-lined plate to drain. Strain the bacon fat, reserving 3 tbsp in the pan.
3) Reheat the bacon fat and fry the potato cubes until light golden brown. Remove to paper towel-lined plate to cool, then season with a pinch of salt.
4) Combine the sour cream, mayonnaise, white vinegar, salt and pepper in a serving bowl. Combine the potatoes and dressing, adjusting the seasoning as necessary. Refrigerate for 1 hour.
5) Chop the bacon and spring onions and use to top the salad before serving.