Preheat the oven to 160°C (fanbake) or 180°C. Line 2 baking trays with baking paper.
In a large bowl, combine all the dry ingredients (except for the baking soda) and stir so they are all mixed together.
In a small saucepan, add the butter and golden syrup and stir over a low heat, until butter is melted. Mix together the baking soda and boiling water, and pour this mixture into the melted butter. Stir together to combine. The mixture should froth a little.
Pour the butter mixture into the dry ingredients and stir to combine. Roll mixture into golf sized balls (slightly smaller) and place on the baking trays spaced about 5-6cm apart to allow for spreading. Flatten each ball slightly (don't flatten them by much, as they will flatten more during cooking).
Place the trays in the oven and bake as follows:For chewy biscuits: 10-12 minutes - remove from oven and cool 5 mins on trays.For crispy biscuits: 15-18 minutes - remove from oven and cool 5 mins on trays.After 5 mins resting on the oven trays, transfer them to a resting rack to cool completely.Remember that every oven is different so check your biscuits either side of these times and know that they will harden on the trays and when resting too.
Anzac Biscuits will keep several weeks in an airtight container (if they last that long!) but I would suggest freezing them after 5 days. The biscuits may soften slightly after a few days.