Break chocolate into pieces and melt in top half of a double boiler over gently simmering water. Pull back husks from Cape gooseberries. Dip halves into melted chocolate; place on baking paper. Leave until chocolate sets.
To make caramel sauce, place sugar cubes, lemon juice and 3 tablespoons water in a saucepan with a heat–proof handle. Boil rapidly until sugar turns golden.
Remove from heat and stir cream into caramelised sugar, taking care not to let it splatter. Immediately pour sauce into a bowl and let cool.
Peel prickly pears, avoiding fine prickles. Cut flesh into thin slices. Arrange prickly pears and star fruit on a platter.
Stir lime juice and icing sugar together and drizzle over fruit. Dust with icing sugar. Drizzle caramel sauce over fruit and garnish with chocolate–dipped Cape gooseberries.