Mix the custard powder, sugar and 6 tablespoons milk. Bring the rest of the milk to the boil. Stir in the pudding powder, bring to the boil again and simmer for about 1 minute while stirring. Allow to cool while stirring several times so that no skin forms.
Finely chop the chocolate. Whip the cream. Fold the chocolate, 2 tablespoons eggnog and half of the cream into the pudding. Pour the cream into glasses. Use the rest of the cream to decorate. Drizzle with the rest of the egg liqueur.