Preheat the oven to 160°C (fan-assisted convection). Grease and line a large tray with baking paper.

Whisk together the egg and sugar (sachet 1) for 1 minute until pale and creamy, then mix in the melted butter and chocolate until well combined. Add the brownie mix (sachet 2) and stir to form a thick batter.

Use a 1 tbsp measuring spoon to scoop portions of batter 5 cm apart on the prepared baking trays. If the batter is too sticky to work with, it can be covered and chilled in the fridge for 10 or so minutes to firm up.

Bake cookies for 10 minutes until cooked on the outside, but still soft in the center. Allow to cool on the trays for 5 minutes before transferring to wire racks to cool.

Tip: Sandwich brownie cookies with a silky buttercream in your favourite flavour, like vanilla, coffee or peanut butter.