Preheat oven to 180°C. Grease and line a 20cm square cake tin (or 2 smaller 10cm square tins).
Place all the ingredients in the bowl of a food processor and process until the mixture is smooth.
Pour into the prepared tin and sprinkle with the extra chopped macadamias. Bake for 15-20 minutes, until a skewer inserted in the middle comes out slightly wet (the brownies will be fudgy).
Allow to cool in the tin for 10 minutes before turning on to a wire rack to cool completely.
Cut into 6 pieces to serve.