Scrape the potatoes under cold water or scrub the skin with a sponge. Cook the potatoes in boiling salted water for 15-20 minutes. In the meantime peel and finely dice the onion.
Cut the olives into slices. Mix vinegar, stock, onion, some salt, pepper and pesto, except for 1 teaspoon. Finally embezzle the oil. Drain the potatoes and mix while still warm with the pesto vinaigrette and the olives.
Soak for about 1 hour and let it cool down. Clean, wash and halve the tomato. Fold the tomatoes into the potato salad and season with salt, pepper and possibly vinegar. Put into a bowl. Stir the sour cream until smooth and add it to the salad as a blob.
Stir the remaining pesto into the Schmandklecks and serve garnished with parsley.