Combine dry ingredients.
Melt the Golden Syrup and butter together. Combine the bicarbonate of soda with the water and add to the butter mixture.
Mix together with the dry ingredients.
Press the mixture into a Swiss roll tin (or for a thicker crunchie, bake in a square 20cm x 20cm tin) and bake for 20 minutes at 150ºC. Gently press down the sides if they seem to rise too much.
When light brown, remove from the oven and cut into squares.
Switch off the oven. Return crunchies to the oven, for about 10 minutes to dry out.
Allow to cool before removing from tin.