Colombian black cake (torta negra Colombiana)

This is Colombia’s version of a rich fruit cake. Dense with prunes, raisins and figs, generously spiked with both rum and port, and cleverly flavoured with aromatic spices, it is hard to stop at one piece. Traditionally dulce quemado (sweet burnt brown sugar), either homemade or bought, is used to sweeten this cake, but molasses makes a perfectly acceptable substitute as I've done in this recipe.