Afters: I thought of doing trusty glamorous fairy cakes with a chocolate topping, and while searching for ganache I found this. So I made two-tone cupcakes with the cake mixes, topped with ganache and a cherry. Based on experience I would modify the recipe a bit as follows:
1) use the traditional mixing method of creaming butter/sugar, mixing in the eggs and milk until smooth, then combining the flour, before proceeding to split the mixture and add the chocolate.
2) do not melt white chocolate in the microwave! Use better quality (Green & Black's?) and melt gently over simmering water.
3) use a lighter chocolate for the ganache, e.g. Green & Black's "darker" milk chocolate, or something else with less than 70% cocoa.
To make the two-tone cupcakes I just dolloped a good spoonful of each mixture into a muffin case, in a tin. One on top of the other, side by side, however it goes. You could marble it with a spoon too. Baking was definitely on the longer side, 25 mins. Lower and slower might help stop them sinking too.