Mix 3 litres of water, vinegar and flour in a wide pot. Wash, peel and clean the black salsifies thoroughly and immediately put them into the vinegar water
Finely dice the bacon. Peel and finely dice the onion. Wash 1 lemon thoroughly, grate dry, peel finely in julienne. Halve lemons, squeeze juice. Chop hazelnuts coarsely
Peel the potatoes, wash them, possibly cut them in half. Cook in boiling salted water for about 25 minutes. Wash the black salsifies again thoroughly, cook in boiling salted water with sugar and about half of the lemon juice for 15-18 minutes.
Wash the fish and dab dry. Wash parsley, shake dry and chop finely. Leave bacon in a pan until crispy. Add 2 tablespoons of oil, heat up, add onions and fry while turning. Add nuts and lemon peel. Deglaze with remaining lemon juice, bring to the boil and season with pepper. Add 25 g butter and heat up. Mix in about 3/4 of the parsley
In the meantime heat 2-3 tablespoons of oil in a frying pan. Fry the fish for 2-3 minutes on each side, season with salt and pepper. Drain the potatoes, add 25 g butter and the remaining parsley, toss briefly with the lid on
Lift the black salsifies out of the water and allow to drain. Arrange black salsify, potatoes, fish and bacon-nut mixture on plates. Add remaining potatoes