Soak gelatine in cold water. Stir the jelly well, except for 4 teaspoons. Stir in yoghurt, crème fraîche and lemon juice
Squeeze the gelatine and dissolve at low heat. Mix first with something, then with the rest of the yoghurt mass. Chill for about 10 minutes. Beat egg whites until stiff, fold in. Pour yoghurt mousse into 4 dessert glasses. Chill for at least 2 hours. Decorate with remaining jelly and chocolate rolls