Turn the oven on to 180°C.
Combine the milk and butter in a large cup and heat in the microwave for 1,30 minutes at 800 W in order to melt butter.
Pour the flour, cocoa, sugar, salt and baking powder into a bowl and mix everything with a whisk.
Make a hole in the center and pour in the vanilla and hot milk.
Mix everything with a whisk to get a lump-free mixture.
Pour the mixture into a buttered and floured 22 cm cake tin.
Bake for 30-35 minutes. (Do the toothpick test).
Remove from the oven and let cool completely.
In the meantime, prepare the ganache: chop the chocolate and pour it into a bowl, add the very hot cream and mix well to get a smooth, shiny cream.
Let it cool for 5 minutes so that it thickens a little.
Turn the cake on a tray and cover with th ganache making sure that it drips a little around the edges.
Cover with chocolate flakes.
Prepare the little monsters by decorating the digetive biscuits with melted chocolate (use a paper cone) and with Smarties as eyes (use a dot of chocolate to make the pupils).
Place the biscuits on the cake just before serving, because the soft and moist base would make them lose their crunchiness!