Preheat oven to 160°C. Line 3 large baking trays with non-stick baking paper. Spread the macadamias over 1 tray ensuring macadamias are no more than two nuts deep and roast until lightly toasted.
When cooled, coarsely chop macadamias on a chopping board.
Sift the flour and sugar into a large bowl. Combine with macadamias, rolled oats and coconut.
To a small jug, add the boiling water, golden syrup and bicarbonate of soda. Once the mixture froths up, add butter and stir. Set aside to cool. Add the slightly cooled butter mixture to the flour mixture, combining with a wooden spoon.
Place two heaped teaspoons of mixture onto baking tray and use the back of a spoon to flatten slightly, spacing 3cm apart. Bake for 15 minutes (or 13 minutes for chewy biscuits). Swap trays around halfway through cooking to ensure trays don’t cook unevenly. Leave on tray for 5 minutes before transfer to wire racks to cool.