Rinse the lamb`s lettuce in a colander under running water, then place in a bowl with water. Finely dice the onion and place in a salad bowl.
Peel the potatoes and cook for about 20 minutes. Pour off the cooking water and place the saucepan on a saucer. Put the butter in the hot pot and wait until it has melted. Then mash the potato with a fork and mix with the melted butter. Put the mashed potatoes in the salad bowl, add the balsamic vinegar, water and mustard and mix together. Season everything well with salt and pepper.
Remove the lamb`s lettuce tufts one by one from the bowl of water, if possible do not pick them apart, just remove bad leaves. Then put the cleaned, still damp / dripping wet salad in the salad bowl. Mix everything together and serve.
Tip:
The potato and balsamic dressing should have a smooth, creamy consistency so that it can mix well with the lamb`s lettuce. If the dressing does not yet have the required consistency, add a little water if necessary. As a rule, however, it will be supple if the lettuce tufts are added dripping wet as described.