Chocolate peppermint crinkle cookie

Mix the cocoa, caster sugar and oil together. Add the egg, whisking until fully combined. Stir the flour, baking powder and a pinch of salt together in a separate bowl, then add to the cocoa mixture and mix until a soft dough forms. Chill for 1 hr if it’s very soft.

Heat the oven to 190C/170C fan/gas 5. Tip the icing sugar into a shallow dish. Scoop a teaspoon of dough and form into a small ball, then roll in the sugar to coat. Repeat with the remaining dough, then arrange, evenly spaced, on a baking tray lined with baking parchment.

Bake in the centre of the oven for 10 mins. Leave to cool on the tray for 15 mins then transfer to a wire rack and leave to cool.

Meanwhile, make the filling. Melt the white chocolate in a heatproof bowl set over a pan of barely simmering water, making sure it does not touch the water, or in the microwave in 30-second bursts until melted. Set aside to cool a little. Beat the butter for 2 mins using electric beaters until smooth and creamy, then beat in the peppermint extract for 30 seconds. Drizzle in the white chocolate and beat until combined. Mix in the icing sugar slowly, then add the food colouring, bit by bit, beating well after each addition until you have a rich, evenly coloured green mix.

Spoon into a piping bag fitted with a round nozzle. Pipe the minty filling onto the middle of a biscuit and gently sandwich with another biscuit. Will keep in an airtight container for four days.