Clean the mushrooms and cut into thin slices. Quarter the apple with the skin, remove the core and also cut into slices.
Fry both ingredients in the butter over a mild heat. Roughly chop the parsley and add.
For the marinade, mix the mustard, salt and sugar, balsamic vinegar, crème fraîche and lemon juice in a bowl. To taste. Fold the lukewarm mushrooms and apple into the marinade.
Spread the cleaned lamb`s lettuce on plates and spread the marinated salad over them.