Preheat oven to 180C and line baking trays with baking paper. Sieve flour, cocoa, bicarbonate of soda and a pinch of salt into a bowl. Beat sugar and butter in an electric mixer until creamy. Add egg and beat to combine. Add flour mixture and stir to just combine, then stir in a third of the chocolate.
Pinch off walnut-sized pieces of dough and place on baking trays, pressing to flatten slightly, leaving a 5cm gap between each. Dot tops with macadamias and remaining chocolate and bake, turning trays partway through cooking, until cookies are set and becoming firm at the edges (12-15 minutes). Cool until firm enough
to transfer to a wire rack, then cool completely (25-30 minutes). Cookies will keep in an airtight container for up to 3 days.