Cream the butter with the sugar (sachet 1) for 1 min until pale, then mix in the egg yolk until well combined. Add the cookie mix (sachet 2) and pistachios and stir to form a smooth dough – you may need to use your hands towards the end to bring it together. 

Shape the dough into a thick log, about 5cm in diameter, and tightly wrap it in a piece of plastic wrap. Firmly twist the ends of the cling film to seal and roll the log along the countertop to smooth out the shape. Place the log in the fridge for 30 min until firm or store in the freezer to bake at a later stage.

Preheat your oven to 160°C (fan-assisted convection) and line two baking trays with baking paper.

Use a sharp thin-bladed knife to cut the log into 5mm-thick slices (see Tip). Place the cookies on the prepared baking trays and bake for 10-12 minutes until crisp. Set aside to cool completely.

Drizzle the melted chocolate over the cookies and sprinkle with the extra pistachios. Once the chocolate has set, store the cookies in a cookie jar or an airtight container.

Tip: If the cookie log crumbles too much when you’re slicing it, set it aside at room temperature to soften a little before trying again.