Preheat oven to 160 degrees Celsius and line a 20x20cm tin with baking paper.
Combine all dry ingredients in a bowl. Use only 200g of the 300g of choc chips.
Combine the butter and golden syrup in a saucepan and stir until melted
add the bicarb of soda to the water and the add it to the butter mixture
When it foams, add it to the dry mixture
Add egg to the mixture and mix until fully combined.
Press into the prepared cake tin and sprinkle with the remaining 100g of chocolate chips.
Cook for 15-20 minutes until golden brown and firm.
Remove from oven and sprinkle with extra salt if you would like. Leave in cake tin until cold.
Once cold, cut into 16 squares and store in an airtight container in the cupboard.