Prepare the shortbread dough – cube the butter into a large mixing bowl, sift in the flour, cocoa powder and a pinch of salt and rub in with your fingertips until the mixture resembles breadcrumbs.
Beat in the sugar & milk, then pull the mixture together with your hands and knead briefly until you have a smooth dough.
Wrap the ball of dough in clingfilm and pop in the fridge to rest for 30 minutes.
While the dough is chilling, preheat the oven to 180°C/350°F/Gas Mark 4. Line 2 large baking trays with non-stick baking paper.
Unwrap the sweets, place in a strong freezer bag and bash with a rolling pin until well crushed. Slice the smarties in half for the penguin beaks.
Once the dough has chilled for 30 minutes, unwrap and turn out onto a well floured surface. Roll out to roughly the thickness a £1 coin.
Using a round cookie cutter, cut out circles of the dough and place them on the lined baking trays. Using a smaller round cutter, cut a circle from each one to form the penguins tummy and remove.
Fill the inner circles with the crushed mints. They should be filled to around the same height as the dough.
Bake the cookies for 10 minutes in the oven, until the mints are completely melted.
Take the cookies out of the oven, and leaving on the trays, immediately add chocolate chips to each cookie – 2 for the eyes and one for the beak. Leave to melt for a minute or so, then add a half a smartie and 2 candy eyes to each cookie – pushing them gently into the melted chocolate chips to stick them on.
Leave to cool until the mints have set, then gently peel from the baking paper and place on a wire cooling rack to finish cooling.
Once completely cool, store in an airtight container until ready to serve.