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 f