Peel and finely chop the onion. Finely dice the gherkins. Clean, wash, drain and roughly chop the rocket. Stir mayonnaise and sour cream until smooth. Stir in onion, gherkins and rocket. Season with salt, pepper, 1 pinch of sugar and lemon juice.
Separate the egg. Stir egg yolk, flour, starch and beer until smooth. Leave to swell for about 15 minutes. Peel potatoes, wash and cook covered in salted water for about 20 minutes.
Wash the fish, dab dry and cut into 4 equal pieces. Season fish with salt and pepper. Beat egg white and 1⁄2 tsp. salt until stiff, fold into the beer batter. Heat the oil in a large pan.
Pull the fish through the beer batter and fry it in hot oil for about 4 minutes on each side until golden brown.
Wash the dill, shake dry and cut finely. Drain the potatoes and mix with the dill. Serve with fish and remoulade. Serve with salad.