For the cream, soak gelatine in cold water. Mix cream firmer and sugar. Mix yoghurt, quark, lemon juice, salt and sugar mixture. Squeeze the gelatine and dissolve. Stir in 3 tablespoons of cream, then stir into the rest of the cream and chill for 20-30 minutes until the cream begins to gel.
Whip cream until stiff and fold in. Add jam and fold in streaks. Pour cream into a piping bag and spread on half the biscuits. Place the remaining biscuits lightly on the cream and chill for 1-2 hours until the cream has set
1 1/2-2 1/2 hours waiting time