Preheat oven to 180°C (160⁰C fan forced). Place butter and sugars in an electric mixer bowl, beat on high until pale (approximately 5 minutes). Add eggs one at a time beating well after each addition.
Sift the flour, cocoa, cinnamon and baking powder over the egg mixture and stir until combined, fold through the chilli flakes and dark chocolate chips.
Place an ice-cream scoop (or roll into walnut size balls) of biscuit dough 4cm apart, on baking paper lined baking trays. Sprinkle a few chilli flakes on each mound of cookie dough.
Bake for 12-15 minutes or until just set, turning tray halfway (they may still seem a little soft). Cool on the tray for 5 minutes, then transfer to a wire rack to cool completely.