Ingredients

Step by step

1. Grease a 20cm x 20cm baking tin and line with baking paper. In a hot pan, heat the walnuts until they smell toasty. Transfer to a chopping board and finely chop, then transfer to a large bowl. Heat the coconut in the same pan until lightly golden. Transfer to the bowl. Pulse the biscuits in a food processor or crush in a food bag using a rolling pin until you have a chunky crumb. Combine the crumbs with the walnuts and coconut in the bowl.

2. Melt 125g of the butter in a heatproof bowl over a pan of simmering water, making sure the bowl doesn’t touch the water. Add the caster sugar, cocoa powder and allspice, whisking well until combined.

3. Remove the bowl from the heat and, whisking continuously, pour in the egg. It will thicken. Return the bowl over the pan of simmering water and continue whisking until smooth and a little thicker, about 30 seconds – don’t worry if the butter separates slightly. Pour the butter mixture over the biscuit mixture and mix well. Pack into the prepared tin, patting down with your hands until you get an even layer. Transfer to your freezer for 15 minutes or fridge for 30 minutes.

4. For the filling, use a stand mixer fitted with the paddle attachment to beat 200g of the butter on a medium speed until smooth. Reduce the speed and add the icing sugar, custard powder and double cream, then beat in the peppermint extract and a pinch of salt. Spread over the chilled biscuit base in a smooth, thick layer. Refrigerate for 2 hours.

5. For the topping, melt the chocolate and remaining butter in a bowl over a pan of simmering water, stirring gently to combine. Leave to cool slightly then spread over the custard layer; gently bang against your work surface to settle the chocolate and ensure it reaches the edges. Refrigerate for 20 minutes, at which point the chocolate should begin to set and be slightly tacky. Score into 16 squares, sprinkle over the sprinkles, and return to the fridge until solid. Using the scored lines, slice into squares with a hot knife.