Galaxy is a hugely popular type of chocolate in the UK and all around the world. I know of people from the UK who have moved overseas and they say Galaxy chocolate is the number one thing they miss! Galaxy has a silky smooth texture and extra rich chocolate flavour that comes from a special cooking process. The makers say this brings out the underlying caramel flavour of the milk chocolate, as well as the comforting taste of warm milk. So, while you can replace the Galaxy in this recipe with regular chocolate, it won't have the same amazing Galaxy flavour.