Place the coffee and 4 tablespoons of the sugar in a shallow dish, pour over the measurement water and stir until dissolved.
Dip 6 biscuits, one at a time, into the coffee mixture, then crumble into the bases of 6 glass tumblers.
Combine the mascarpone with the remaining sugar in a bowl, then gradually whisk in the cream until smooth. Stir in the kirsch, if using, then divide half the mixture between the glasses.
Crumble half the raspberries over the top of the mascarpone mixture in the glasses, then sprinkle with half the chocolate. Dip the remaining biscuits in the coffee mix, crumble and add to the glasses.
Add the remaining mascarpone mixture and whole raspberries to the glasses, finishing with a sprinkling of the remaining chocolate. Serve immediately or chill until required.