Edible soil and decorations

• Blitz the chocolate biscuits (the ones without cream filling) to fine crumbs and tip them into a bowl.
• Make a small batch of thick icing from icing sugar and a little water – it acts as glue for the eyes and hair on the marshmallows – and the Oreos. These can be prepared earlier in the day or the day before.

  Dab a little icing on the back of the sugar eyes and place two on each Oreo and two on each marshmallow. Brush the tops of the marshmallows with a little icing too, and dip them in the blitzed chocolate biscuits. Save the rest of the crumbs to sprinkle over the top of the cake.
• Put the ingredients for the cream in a bowl and whisk them together with a hand mixer until the cream thickens.

  The cream needs to be firm enough to hold the toppings in place on the cake, but take care not to overwhip it.
• Divide the cocoa cream between the 2 mazarin tarts and spread it out well so the whole cake is covered.
• Sprinkle the tops with the blitzed biscuits and arrange the marshmallows and Oreos on top. Press them gently into the cake, and if needed use a little of the leftover cocoa cream from the bowl to "glue" them to the cake.

  If the marshmallows are too large, you can halve them lengthways (vertically, through the height) so you get two tall, slimmer halves.
• Finally, melt 2-3 marshmallows in the microwave – they need about 10-15 seconds on full power.

  Stir with a spoon until you have a sticky mass, then use the thumb and index finger of both hands to pull cobwebs across the cake. Stick the ends to the side of the cake. It's sticky – but just look how good it looks ;-)
• Serve the cake straight away – or keep it in the fridge for a couple of hours.