Step 1

Preheat oven to 180C/160C fan forced. Line 2 baking trays with baking paper. Use electric beaters to beat the butter and icing sugar in a large bowl until smooth and creamy. Beat in the vanilla.

Step 2

Use a large metal spoon to fold the flours and cocoa into the butter mixture. Using lightly floured hands, roll table-spoonfuls of the mixture into balls. Place on the prepared trays, allowing room for spreading. Use a lightly floured fork to flatten. Bake for 15-20 minutes or until firm. Set aside to cool completely

Step 3

For the filling, use electric beaters to beat the butter and icing sugar in a bowl until pale and creamy. Beat in the chocolate until smooth. Spoon into a piping bag fitted with a 5mm star nozzle. Pipe mixture over half the biscuits. Top with the remaining biscuits.

Step 4

Drizzle the biscuits with the melted chocolate, if using.