Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Wash and clean the zucchini and use a slicer to slice them lengthwise into 1-2 mm thin slices. Season with salt and pepper.
Wash the fish, dab dry and cut the fillets in half lengthwise. Wash the chervil, shake dry and, except for something to garnish, pluck the leaves from the stems and chop them. Wind 1/2 plaice fillet and 1 slice of courgette tightly together and pin with wooden skewers.
Spread on a greased baking tray and spread Hollandaise sauce on the rolls. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 10 minutes. Switch on the grill for the last 3 minutes.
Wash, clean and slice the tomatoes. In the meantime heat milk and butter. Drain potatoes, add milk-butter and season with salt and nutmeg. Stir in chervil. Mash to puree.
Arrange mashed potatoes, tomatoes and plaice rolls on plates. Garnish with chervil.