Wash the potatoes and cook in boiling water for 15-20 minutes. Rinse the potatoes under cold water and remove the skin. Melt 20 g butter, toss the potatoes in it and keep warm. Wash the pike-perch fillet, dab dry and cut in half lengthwise. Cut fillets into 50-75 g portion pieces and salt them.
Put Riesling in a high pan and bring to the boil briefly. Place the pike-perch fillets in the pan, cover them and let them simmer for about 3 minutes on each side at low heat. Place the pike-perch fillets on a preheated plate and keep warm. Pour cream into the wine and let it boil down to about 2/3. Sort sorrel, cut off stems except for a few leaves for garnishing and wash the leaves. Drain sorrel and cut into fine strips. Cut 50 g cold butter into cubes and gradually stir into the sauce with a whisk. Do not let it boil any more. Add sorrel and season the sauce with salt, pepper and some lemon juice. Arrange pike-perch with sorrel and Riesling sauce and small buttered potatoes on plates.
Drain sorrel and cut into fine strips. Cut 50 g cold butter into cubes and gradually stir into the sauce with a whisk. Do not let it boil any more. Add sorrel and season the sauce with salt, pepper and some lemon juice. Arrange pike-perch with sorrel and Riesling sauce and small buttered potatoes on plates. Serve immediately garnished with sorrel leaves and lemon. Serve with green salad