Mix 2 litres of water, vinegar and flour in a wide pot. Wash and peel the black salsifies thoroughly, cut off the ends and put them immediately into the vinegar water.
Halve the lemons, squeeze the juice. Wash the black salsifies again thoroughly, cut them into pieces about 5 cm long, put them in boiling salted water with about half the lemon juice and 1/2 tsp. sugar and cook for about 15 minutes.
Wash parsley, shake dry and pluck leaves from the stalks. Chop leaves. Season remaining lemon juice with salt and pepper. Fold in olive oil. Stir in parsley.
Heat sunflower oil in a frying pan. Drain the black salsifies, drain well and fry in the pan for approx. 5 minutes, turning over. Add 50 g sugar and caramelise. Remove the black salsifies, mix with the vinaigrette and serve.