Put the chocolate in a heatproof bowl. Place in a bain-marie (over a saucepan of simmering water), and mix until melted. Heat the milk in a small saucepan until boiling. Pour into the melted chocolate and stir well. Add the liqueur and blend until smooth.
Remove from the heat. Gradually add the apricot pieces, stirring constantly. As the mixture cools it will thicken and form a workable paste. Allow to cool so that you can roll the mixture into balls between your fingers. Leave to cool completely, while you temper the couverture for dipping.
Sift the cocoa powder on to a plate. Using a thin fork, stab the truffles one at a time, dip in the tempered chocolate, then roll in the cocoa powder and leave to cool.