Peel and finely chop the onion. Rinse crabs briefly in cold water and drain well. Mix mayonnaise, cream and diced onion. Season with salt, pepper, lemon juice and sugar. Leave to stand for about 1/2 hour.
Then season again to taste. Clean and wash the salad leaves and pluck them into bite-sized pieces. Clean, wash and slice the tomatoes and cucumber. Wash parsley, dab dry and chop finely, except for a little to garnish.
Cut salmon into bite-sized pieces. Arrange the prepared ingredients with the sauce and the salmon in portions. Sprinkle with parsley and serve garnished with lemon and parsley leaves.