Soak the gelatine in cold water. Peel the eggs and dice them with an egg cutter. Mix the yogurt, sour cream and mayonnaise with the herbs and spices. Melt the squeezed out gelatine, stir in some yoghurt mixture. Then add the gelatine to the rest of the yoghurt mixture and chill.
When the mixture starts to gel, fold in the finely diced eggs. Chill until serving.
At the table, use a tablespoon dipped in hot water to peel the nocks off the egg mousse, place on a plate and decorate with cress.