Peel and thinly slice potatoes. Just cover with cold, salted water and bring to the boil. Cook until just tender, about 10 minutes. Don't overcook or the potatoes will tend to go mushy. Drain, and place in a bowl. Put oil, freshly ground black pepper, dill, vinegar and mustard into a blender and mix well. Add salad burnet to vinegarette and pour over the potatoes while still warm and serve. This dish can be served cold with good results.