Peel the onion leaving it whole. Slice into rings and place in a mixing basin. Cover with boiling water and allow to soak for 2 minutes. Drain and chill.
Peel and core the apple and dice into a basin. Sprinkle with the lemon juice and toss the apple pieces. Add the onion rings, the soured cream and a seasoning of salt and pepper. Toss the ingredients to mix.
Drain the herrings from any liquor and open out. Arrange the herrings flat on individual serving dishes with the flesh side uppermost. Spoon the apple and onion and soured cream mixture over the top and serve.