How to make
First, make the cream. Heat the milk with the sugar. Dilute the flour and cocoa with a little water to create a sludge.
Once the milk comes to a boil, pour the sludge in a thin trickle and stir until thickened. Remove from the stove and add the butter. Lay out a rectangular cake form with foil.
Arrange a layer of the 8 biscuits, pour part of the cream on top. Arrange cake biscuits on top, then cream and more biscuits until you run out and fill the entire form.
Wrap up the roll using the foil and place it in the fridge to cool. After an hour, invert it onto a plate, remove the foil.
Beat the cream with a mixer, set aside a bit for decorating the top. Mix the rest with the 2 tbsp melted chocolate and smooth out the sides. Sprinkle the walnuts on top. Pour the set aside cream into a pastry bag and decorate the roll on top.
Sprinkle with the grated chocolate and leave overnight in the fridge. The next day, slice it and serve with a cup of coffee.
