Grease an 8-inch square cake pan. Fill a bowl with cold water.
Bring sugar and golden syrup to a boil in a large saucepan over medium heat. Reduce heat and simmer until a small amount of syrup dropped into the water turns brittle, 10 to 15 minutes.
Remove from heat and carefully add baking soda; stir quickly until foaming subsides and mixture turns golden. Pour into prepared cake pan. Cool until set, about 15 minutes. Break into bite-size chunks to serve.