Before you begin, select an appropriate mould for your chocolates (I find that ice cube trays work well), and dust them with cocoa or ground coffee.
Break the white chocolate up in to a measuring jug and place the jug in a pan of simmering hot water. Stir continually until all the chocolate has melted.
Carefully spoon melted chocolate in to each mould (while trying to make less of a mess than I did).
Gently place a small ball (I used beads) in to each mould, in the center of each chocolate and push down a little, but not too much as to touch the bottom of the mould. Leave to set.
When the chocolate has set, remove the balls. This can be quite tricky, I found the best way was to stick a paper clip inside the holes of the beads and yank them out.
Fill each chocolate crater with a small amount of coffee liqueur. The alcohol wont freeze, but I placed the chocolates in the freezer for a few minutes to help out with the next part (I'm not entirely sure why, but it worked well).
Now break the milk chocolate in to a measuring jug and melt like before.
Now, here's the tricky bit. The best way to add the chocolate, without disturbing the liqueur, is to take a big spoonful of chocolate and dump it straight on top, smooth down carefully and leave it to set. You have to work pretty quickly at this point.
When the chocolate has set, remove the chocolates from the moulds and enjoy!