For the cheddar crust, wash parsley, shake dry, pluck the leaves and chop finely. Dice the cheddar finely. Mix 100 g butter, breadcrumbs, parsley and egg and stir in the cheese. Season with salt and pepper.
Spread a piece of cling film on the work surface. Spread the crumb mixture on it to form a rectangle (approx. 15 x 30 cm). Wrap the foil over it and carefully smooth it out again with a pastry roll. Chill the mixture for at least 30 minutes.
Clean and wash the cauliflower and divide it into small florets. Cook in boiling salted water for about 5 minutes. Drain, rinse with cold water and let drain. Cut ham into strips. Peel and wash the potatoes and cut them into pieces. Cook in boiling salted water for about 20 minutes.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line a baking tray with baking paper. Rinse fish, pat dry, season with salt and pepper. Place the fish on the baking tray. Divide the breadcrumbs into 4 pieces. Distribute on the fillets. Bake in a hot oven for 15-20 minutes.
Drain the potatoes and let them evaporate briefly. Bring 100 ml water and cream to the boil, stir in the stock. Add to the potatoes and mash to puree. Season to taste with salt.
Roast the hazelnuts in a pan without fat and take them out. Heat 2 tablespoons of butter in the hot pan. Sauté the cauliflower for about 3 minutes, season with salt. Arrange puree and fish on plates. Arrange cauliflower, ham and hazelnut leaves around them. Cut cress from the bed and sprinkle over it.