Step 4: Layer 2, the milk chocolate middle
Make the milk chocolate ganache in exactly the same way as the dark chocolate (melt the chocolate and stir in the cream), but don't put it away to set. Instead, use it immediately to coat the dark chocolate centres in a layer of milk chocolate.
You can do this by putting the ganache in a deep bowl and dipping the truffles in, though when I try this I lose things to the chocolatey depths. An easier but messier method is to half dip them, put them wet side down on the tray, and then spoon more ganache over the top. Put them back in the fridge for this layer to set.
Neatness isn't important right now, since once the truffles are set they can be re rolled into neat balls. Once again use cocoa powder to keep yourself relatively mess free.