For the potato soufflé, peel and dice the potatoes and cook in a perforated cooking container (at 100°C for 9-10 minutes or at 120°C for 4-5 minutes).
Press potatoes through a potato ricer. Mix yolks, coarsely chopped chervil, sour cream and peas and season with salt, pepper and nutmeg.
Fold in stiffly beaten egg whites and pour mixture into buttered baking cups dusted with cornstarch. Sprinkle with Parmesan cheese.
Cover the ramekins with aluminum foil, place in the cooking container and cook (at 90°C for 30-35 minutes).