Melt the plain dark chocolate in a bowl over a pan of simmering water (see
Divide the chocolate into 2 rectangular sealable containers. Add the cream liqueur to one container and the coffee liqueur to the other and mix each in well. Chill for at least 2 hours until firm.
Use a melon baller or 2 teaspoons to scoop out 6 cream liqueur truffles and arrange them on a paper-lined nonstick baking sheet. Repeat with the coffee liqueur truffles.
Melt the milk chocolate in a bowl over a pan of simmering water. Stir well, then, holding 1 truffle at a time on a fork over the bowl, spoon melted chocolate over the top to coat it. Place each truffle on a piece of waxed paper on a nonstick baking sheet. Press a chocolate coffee bean into the top of each truffle.
Leave the truffles for at least 1 hour, until the coating has set. Put them in petit-four cases and pack into a gift box or tin.