Slide the baking tray into the oven. Preheat oven (electric cooker: 250 °C/ circulating air: 225 °C/ gas: level 5)
Clean, wash, drain and chill the lamb's lettuce. Season vinegar with salt, pepper and 1 pinch of sugar, add oil. For the crust cut 60 g fat into pieces. Grind toast finely in the universal chopper. Wash parsley, shake dry and chop finely. Put everything in a bowl and mix. Peel and wash the potatoes and cook in boiling salted water for 15-20 minutes
Wash the fish, dab dry and cut into 4 equal pieces. Cover with the crust. Take the tray out of the oven and spread with fat. Place the fish on top and cook for 12-15 minutes on the middle shelf until the crust is golden brown
Melt 40 g fat in a saucepan, sprinkle flour over it, sweat it on and deglaze with milk while stirring. Add fish stock, white wine and lemon juice, bring to the boil and simmer for about 5 minutes. Stir in lobster paste and season with salt and pepper. Drain the crayfish tails, add to the sauce and simmer for 2-3 minutes
Drain the potatoes. Remove fish from the oven and arrange on plates with potatoes and sauce. Place salad in bowls and drizzle with vinaigrette