• Preheat your oven to 180°C (160°C for a fan-assisted oven, Gas Mark 4 or 350°F) and line a couple of baking trays with greaseproof paper. Set aside.
• In a large bowl, cream together your butter/margarine and sugar until light & fluffy in both colour and texture.
• Add your egg and stir through until combined.
• Sift in your flour and cocoa powder. Stir through, then use your hands to bring the ingredients together and create a dough. Gently knead the dough on a work surface until it is smooth.
• Place the dough between two sheets of greaseproof paper. Using a rolling pin, roll the dough to around 5mm-1cm (¼-½ inch) thickness before cutting your biscuits with a cookie cutter to your desired size. Transfer the cut biscuits to your pre-lined baking trays.
• Bake your biscuits in your preheated oven for 10-15 minutes, until they appear dry on top. Times will depend on your biscuit size - less for smaller biscuits, longer for bigger ones.
• Once your biscuits are cool enough to handle (but still warm), spread the Nutella on the underside of half your biscuits, using about a teaspoon of Nutella for each biscuit. Pop the other half of the biscuits on top of these and sandwich them together. When your biscuits are completely cool, prepare your icing.

For the Decoration

• In a small-to-medium bowl, mix your icing sugar with a few tablespoons of hot water until you have a slightly runny but somewhat "gloopy" consistency. Remove a couple of tablespoons of your icing into a separate bowl, and mix with your black food colouring. Transfer the black icing to a piping bag and set aside.
• Once your now-filled biscuits have cooled completely, gently dip the top of each sandwiched biscuit into your white icing, holding it over the bowl for a moment to let the excess icing drip off.
• Using your black icing, pipe a few circles on top of your white icing, finishing with a decent-sized dot in the centre. With a cocktail stick, drag around half a dozen lines from the middle dot, through the circles to the biscuit edge. This will make your spider web design. Allow the icing to set for a couple of hours before enjoying.