For the cakes:
I make this in two 5 inch round tins, and then split each into two to make four layers. Line and grease the tins. Preheat the oven to 180C. Cream the softened butter and sugar together until pale and fluffy. Add the egg and beat in. Sieve the flour, baking powder and Horlicks into the bowl and then fold in until nearly combined. Add the milk and fold again, then finally add the boiling water. Quickly spoon into the tin and put in the oven. Bake for about 20-25 minutes or until deep gold and a skewer comes out clean.
For the ganache:
Break the chocolate up into small pieces and put into a bowl. Heat the cream then pour over the chocolate. Leave for a few minutes and then beat in.
Split the cakes carefully into two. Sandwich them with some of the ganache, then cover with a crumb coat. Put it the fridge to set slightly. While it is cooling, chop the maltesers - I found using a sharp knife in a quick decisive motion worked best. Remove the cake from the fridge and use the remaining ganache to cover the cake. Starting from the top, arrange the maltesers in the desired pattern, then go down the sides, being careful when placing the pale-side-out halves. Put in the fridge for ten minutes or so, then serve. Best eaten on the day, due to the malteser insides getting damp and disintegrating!