Dice the cheese. Wash the watercress and pimpinella, shake dry and chop coarsely. Clean, wash and slice the mushrooms. Whisk eggs, cream and herbs. Season with salt, pepper and nutmeg.
Heat 1 tablespoon of butter in a pan (approx. 20 cm Ø; e.g. cast iron). Fry the mushrooms for about 3 minutes. Season with salt and take out.
Pour half the egg mixture into the pan and let it set for about 5 minutes. Spread half the cheese and half the mushrooms on the omelette, then cover and allow to set for about 1 minute. Fold the omelette and keep warm.
Bake another omelette from the remaining ingredients.