Clean the red cabbage and fennel and cut into fine strips. Knead cabbage, fennel, vinegar, jelly, 1 teaspoon of oil and approx. 1/4 teaspoon of salt and leave to stand for approx. 1 hour
Separate 1 egg. Stir egg yolk, 75 g flour, starch and beer until smooth and let it swell for about 15 minutes. Peel onion and chop finely. Drain cucumbers and chop finely. Chop capers finely. Stir mayonnaise and sour cream until smooth. Stir in onion, capers and cucumber. Season to taste with lemon juice, salt and pepper
Peel the vegetable onion and cut into thick slices. Divide slices into rings. Beat 1 egg and milk in a bowl and season with salt and pepper. Put 50 g flour and breadcrumbs also in a deep plate. Turn onion rings first in flour, then egg and finally breadcrumbs
Beat the egg white with 1/2 teaspoon salt until stiff and fold into the beer batter. Wash the fish, dab dry and cut into 6 pieces. Remove any bones. Season with salt and pepper. Heat oil in a large pan. Pull the fish through the beer batter and fry it in the hot oil for about 4 minutes on each side until golden brown
Drain fish on kitchen paper, keep warm. Fry onion rings for 2-3 minutes until golden brown. Halve the rolls and spread with the tartar sauce. Add the fish, then spread the red cabbage salad on top. Arrange the fish burger, onion rings and possibly some salad
Waiting time approx. 30 minutes