Boil the pudding according to packet directions with the milk and sugar. After it thickens add the butter and stir until melted.
Mix the milk and sugar that you'll use to dip the biscuits, stir until melted.
Put plastic wrap in a rectangular cake form, have the edges spill out on all sides. Pour in 1/2 the pudding in the form, even it out.
Dip each biscuit in the cold milk, smear on one side with chocolate spread and arrange vertically on top of the pudding cream, starting from the long side of the form.
Arrange until you've filled the form, pour on the 2nd half of the cream, even it out.
Wrap the biscuit cake with the wrap that's spilling out on both sides and place in fridge for 60-90 min.
Take the cake out of the form, invert it onto a suitable plate and remove the plastic wrap.
Make the glaze by melting the crumbled dark chocolate and butter in a water bath to a smooth mixture.
Once cooled a bit, pour the glaze evenly on all sides and put in the fridge for the glaze to harden.