Crush the biscuits, place in a bowl. Mix in the butter, transfer to the prepared tin, flatten with the base of a glass. Spread the apricot jam over the top.
Combine the quark, yoghurt and icing sugar. Dissolve the gelatine in water, stir in 2 tbsp of the quark mixture and immediately stir into the remaining mixture. Spread the quark mixture over the base. Leave to set for approx. 6 hrs. or overnight.
Bring the cream, cocoa powder and butter to the boil, remove from the heat, allow to cool slightly. Add the chocolate, melt and mix together. Stir in the icing sugar. Remove the quark cake from the tin, slide onto a rack, pour the icing over the top.
Mix the icing sugar and water, transfer to a piping bag, cut off the tip. Pipe onto the cake in a spiral design. Drag a small skewer from the centre to the edge to create a spider web design.