When testing this recipe first time around I did use a dark chocolate ganache inside of the cake. In all honesty, it dominated the rest of the flavours. It was just too rich for the rest of the Baileys cake. For this reason, I do not recommend using a dark chocolate ganache I've added just a small hint of dark chocolate alongside the milk chocolate in the ganache recipe. This is to ensure that the overall ganache is not too sweet. It's perfect.