First cook a pudding from milk, sugar and pudding powder according to the instructions on the packet. Stir the coarsely chopped chocolate into the hot pudding and let the pudding cool, possibly cover with foil so that no skin develops. Otherwise, peel off the skin after it has cooled down.
After cooling, stir the pudding until smooth. Stir the finely grated chocolate into the pudding.
Beat the cream with the cream stiffener until stiff. Carefully fold in the liqueur. Now layer everything in 4 glasses (pudding-cream-pudding-cream) and decorate as desired, e.g., with cream dots, chocolate shavings and an ice cream cone, there are no limits to the imagination. Chill until serving.
A variant for those with a sweet tooth: use vanilla or cream pudding and white chocolate instead of bittersweet!