For the potato salad marinade, put some water in a saucepan, peel and finely dice the onion and bring to the boil with mustard, pepper, salt, sugar and vinegar.
Boil the potatoes until tender, peel them while still hot and cut them into slices. Pour the marinade over the still hot potatoes and mix well. Let it steep for about an hour. Pour plenty of oil over it and let it rest again. If necessary, season with salt, pepper, vinegar or even sugar.
Just before serving, mix the cleaned iceberg lettuce, cut into small pieces, into the potatoes.
* Link to supply: Medium hot herb mustard and spice mixes: granulated vegetable broth