Preheat an oven to 180°C (355°F). Line two baking trays with baking parchment.
Melt the butter and chocolate in a heatproof bowl over a pan of barely simmering water, making sure the bowl does not touch the water. Remove from the heat and allow to cool slightly.
Whisk the sugar, eggs and vanilla in a separate bowl for about three minutes or until light, fluffy and pale in colour, then fold in the chocolate mixture.
Sift the flour, cocoa and baking powder together and fold into the mixture.
Place tablespoons of the mixture onto the baking trays (the mixture should make about 20
biscuits) and bake for 10–12 minutes. Remove from the oven and allow to cool.
For the filling, cream the butter, sugar and milk together. Add a few drops of peppermint extract to taste. If desired, finish with a few drops of the natural food coloring until you’re happy with the final color. Cream everything together until light and airy.
When the pies have cooled, pair them up and apply a layer of filling to one of the flatter sides and sandwich them together. Dust with icing sugar.