Wash the plaice fillets, dab dry and sprinkle with lemon juice. Leave the fish to stand for a short time. In the meantime peel the shallots for the marinade. Bring vinegar essence, 1/2 litre water, shallots, peppercorns, mustard seeds, chilli and salt to the boil and cook for 5-8 minutes at medium heat.
Wash the tarragon and dab dry. Pluck off the leaves, except for something to garnish, and add to the hot marinade. Leave to cool. Mix flour and 1 teaspoon of salt and turn the plaice in it. Shake off excess flour.
Heat 20 g of fat in a pan and fry the plaice fillets in portions until crispy brown. Put them on kitchen paper and let them cool down. Place the plaice in a flat, wide form and pour the vinegar stock over them.
Leave covered for at least 24 hours. Serve garnished with fresh tarragon.