Makes 12
- 230g unsalted butter, room temperature
- 150g brown sugar
- 110g caster sugar
- 2 free-range eggs, room temperature
- 485g plain flour
- 2 tbsp cornflour
- 2 tsp bicarbonate of soda
- 25g cocoa powder
- 90g unsalted butter, room temperature
- 250g icing sugar, sifted
- 30g cocoa powder, sifted
- 1 tbsp malted milk powder
- 80ml full-cream milk
- 200g dark chocolate (50-60% cocoa solids)
- 1 tbsp coconut oil
In a bowl of a stand mixer fitted with a paddle attachment, mix the butter, brown sugar and caster sugar for three minutes, then add the eggs and mix for a further five minutes until the mixture looks smooth, pale and fluffy. Add the plain flour, cornflour, bicarb soda and cocoa powder, and mix until just combined.
Press the dough out into a disc (this will make it easier to roll out later), wrap in a tea towel and refrigerate for at least one hour or ideally overnight.
Preheat the oven to 180C. Line a baking tray with baking paper.
Place the dough between two sheets of baking paper and roll out into a 5mm-thick sheet. Remove the paper, and cut the dough into four 8cm rectangles, and place on your baking tray. Bake for 10–12 minutes, then transfer to a wire rack and allow the biscuits to cool completely.
To make the chocolate buttercream, mix the butter in the bowl of a stand mixer fitted with a paddle attachment for two minutes or until smooth. Add the icing sugar, cocoa powder and malted milk powder, and mix on medium speed for three minutes or until smooth and fluffy.
With the mixer running on low speed, slowly pour in the milk and continue mixing for two minutes or until the mixture is well combined, scraping down the sides as needed. Transfer the mixture to a piping bag fitted with a 1cm nozzle.
To make the chocolate topping, combine the chocolate and coconut oil in a bowl over a double boiler, and stir continuously until you have a smooth mixture. (Alternatively, you can melt the mixture in the microwave, stirring in 30-second intervals, until it is smooth.)
To assemble, pipe the buttercream filling on to a biscuit and place another biscuit on top to create a ‘sandwich’. Over a wire rack, spoon over the chocolate topping over the top and sides and allow to set.