Peel, wash and halve the potatoes and cook them covered in salted water for about 20 minutes. Clean, wash and divide Romanesco into florets.
Drain the potatoes, let them steam briefly and press them hot through a potato press. Stir in 2 tablespoons of butter and 2 egg yolks. Season with salt and nutmeg. Pour the potato mixture into a piping bag with a large star-shaped spout, allow to cool slightly.
Wash the fish, dab dry and cut into 4 equal pieces. Wash the dill and cut finely.
Spray tuffs from the potato mixture onto a baking tray lined with baking paper. Whisk 1 egg yolk and 2 tbsp. cream. Carefully brush the tuffs with the mixture. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for about 15 minutes.
Heat the oil in a large frying pan. Fry the fish in 2 portions on each side for 2-4 minutes, depending on the thickness, frying the pike-perch on the skin side first. Season with salt and pepper. Remove and keep warm.
Cook Romanesco in boiling salted water for 8-10 minutes. For the saffron sauce, put the rest of the cream and 1⁄8 l water in a pot. Stir in sauce powder and saffron. Bring to the boil briefly while stirring. Beat 50 g butter in pieces and remove from the heat.
Add crabmeat to the sauce.
Drain the Romaneso and add 1 tablespoon of butter, flick through. Serve the fish with sauce, Romanesco and duchess potatoes. Sprinkle with dill.