Cut the plums in half and remove the stones. Put them in an ovenproof dish, snuggled up together. Scatter over the blackberries and trickle over the brandy or kirsch.
Place a tsps of Mascarpone in each hollow and sprinkle over the sugar.
Place under a preheated hot grill for about 5-8 minutes until the sugar melts and the cream cheese runs. Eat warm.