Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Melt the fat in a saucepan. Sweat flour in it. Deglaze with milk, stir in Qimiq and simmer for about 2 minutes, stirring occasionally.
Season with salt and pepper. Clean, wash and drain the salad. Peel onions. Chop 1/2 onion finely, cut 1 1/2 onions into thin slices. Season vinegar and 1 tsp. water with salt, pepper and sugar.
Add 1 teaspoon of oil. Mix onion slices and salad in a bowl. Wash the fish and dab dry. Season with salt and pepper. Heat 1 tablespoon of oil in a coated pan. Fry the fish for 3-4 minutes on each side.
Wash the dill, dab dry, pluck flags from the stems. Put 4 flags aside for garnishing, cut the rest finely. Wash lemon, grate dry, cut into slices. Drain the potatoes, add to the sauce with the dill and simmer briefly.
Arrange salad in bowls and drizzle with vinaigrette. Season potatoes with salt and pepper again. Arrange fish, potatoes and sauce on plates. Sprinkle with diced onion and garnish with the rest of the dill.
Add lettuce and lemon wedges.