I haven't done a tremendous amount of fiddling with this, but I did once make it, for friends who are more chocolate-crazed than I am, by replacing 25g / 3 tablespoons of the flour with good cocoa powder (not drinking chocolate) and adding 100g / 4oz of dark chocolate, cut up into smallish chunks. And you could just as easily use the chocolate chips sold in the baking aisle of supermarkets. If you're thinking about giving this cake to children, don't worry, the alcohol doesn't pervade: you just end up with stickily, aromatically swollen fruit.
Photo by Petrina Tinslay.
Recipe posted by Nigella