Wash the potatoes and cook in boiling salted water for 15-20 minutes. In the meantime, roast mustard seeds in a pan without fat until golden brown. Wash the herbs and cut them finely, except for a little garnish.
Mix crème fraîche, sour cream, herbs and mustard seeds. Season with salt, cayenne pepper and mustard. Peel the potatoes. Serve with cream dip and salmon on the salad leaves. Garnish with remaining herbs and lemon slice.