Heat up the milk, add the sugar and stir until it melts.
Dissolve the packet of starch in a little of the milk, stir and pour it in a thin trickle to the milk.
Stir energetically until you get a smooth cream. Arrange the biscotti in a cake form, smear them with the cream, keep arranging until you run out of cream.
Grate the chocolate on a coarse grater over the still-warm cake so it melts slightly.