Step 1

Sieve the flour, cocoa powder, bicarbonate of soda and a pinch of fine sea salt into a bowl. Whisk together, then set aside. In a separate bowl, use electric beaters to cream together the butter and sugar until light and creamy (about 3 minutes). Add the flour mixture and mix together just until combined. It may look a touch dry (but not floury); if you squeeze some of the mixture it should hold together.

Step 2

Use your hands to bring the dough into a ball. Put it between 2 sheets of baking parchment and roll out until about 0.4cm thick. Slide the dough (and parchment) onto a baking tray and chill for at least 1 hour, until firm.

Step 3

Preheat the oven to 180ºC, gas mark 4. Line 2 large baking trays with parchment. Peel the top sheet of parchment off the dough and use a 4cm round cookie cutter to cut out as many biscuits as you can, putting them on the baking trays. Gather the scraps and re-roll to make 24 biscuits in total. Bake for 10-12 minutes (you may need to do this in batches), until dry and crisp at the edges and fully set in the middle. Allow to cool fully on the baking trays.

Step 4

For the filling, use electric beaters to beat the butter, zest and a pinch of salt until soft and creamy, then slowly beat in the icing sugar. Once all the sugar has been added, increase the speed to high and beat the buttercream mixture until light and fluffy (up to 5 minutes). Add the orange juice and food colouring, if using; beat briefly until fully combined. Spoon or pipe a round of buttercream onto the back of ½ the biscuits and sandwich together with a second biscuit.

Step 5

To decorate the biscuits, melt the white chocolate in a bowl set over a pan of simmering water. Once the chocolate is melted, remove from the heat and set aside for 10 minutes until slightly thickened. Add the filled biscuits one at a time to the chocolate, using a fork to dunk them to coat completely. Use the fork to lift them out, allowing the excess chocolatemto drip back into the bowl. Set the biscuits on parchment and top each with 2 edible eyes. Once all the biscuits are coated, chill for 15 minutes, until set. Remelt the remaining chocolate if necessary over a pan of barely simmering water and use a piping bag with the end snipped off to pipe random lines over the biscuits , avoiding the eyes. (Alternatively, drizzle over with a spoon.) Chill until set. They will keep in the fridge for 4-5 days.