Heat 100 ml (3½ fl oz) cream in a small pan with the milk, sugar, 1 tablespoon chocolate liqueur and the chocolate, gently stirring until the chocolate has melted. Bring to the boil.
Remove the pan from the heat, sprinkle over the gelatine and leave for 5 minutes. Stir together, add the vanilla extract and mix. Strain the mixture into a jug.
Grease and line 2 x 150 ml (¼ pint) pudding basins with clingfilm. Pour the mixture into the prepared pudding basins and chill for 2 hours.
Turn on to plates and remove the clingfilm. Mix together the rest of the cream and chocolate liqueur and drizzle around the panna cotta. Finish with a white chocolate coffee bean on each.