Prepare a square tray 8 3/4″ (22 cm) per side. It's best to leave the ingredients at room temperature before you begin making the dessert.
For the layer:
Melt the butter in a water bath with the sugar and cocoa, stirring nonstop. The butter and sugar need to melt well. Pour the egg (whipped beforehand) in a thin trickle. Stir until thickened, then remove from the heat.
Grind the biscuits, walnuts, raisins in a nut chopper.
Lay out a sheet of transparent foil in a small, square tray. Place it so that part of its edges spill outside the walls of the tray. Pour the mixture in, spread it out and even it out lightly with a spoon.
Put the tray in the fridge for 30 min. to harden.
In the meantime you can make the cream mixture:
Beat the confectionery cream with a mixer. Beat the butter and powdered sugar in a separate bowl. To the butter, start adding the confectionery cream spoon by spoon. Also add the powdered vanilla cream. Finally, gradually add the milk as well. Beat everything with a mixer to a fluffy cream.
Pour this cream mixture over the cake layer and return it to the fridge.
For the chocolate cream:
Make a ganache as follows: Place a container in another container in a water bath. Crumble the chocolate into cubes into it and leave them to melt. Pour the cream and milk into the chocolate. Stir until it becomes a very smooth mixture. Remove from the stove and once it cools but while still runny, pour it over the cake. Smooth it out, make wavy lines along the surface with a fork.
Return the cake to the fridge to set for 30-40 min.
Before serving, you can take the cake out of the form by transferring it to a platter with the foil. Then, carefully unstick and remove the foil.
Cut the cake into smaller squares. To make it easier to cut the chocolate topping without ruining it, it's best to do this with a hot knife before serving. You can heat the knife by dipping it in hot water.
It's also good to leave the Nanaimo desserts to sit at room temperature for awhile before serving. This allows the biscuit-cream-chocolate layers to soften to make it even more pleasant to the taste.
Decorate as desired. Serve with a strawberry rose.