Grease a rimmed 8x12-inch baking pan and line bottom and sides with parchment paper, making sure the parchment sides reach at least 2 inches above the sides of the baking sheet. Grease parchment with butter.
Combine sugar, golden syrup, water, and vanilla extract in a deep, heavy-bottomed saucepan. Bring to a boil, but do not stir. Heat to 310 degrees F (155 degrees C) or until a small amount of syrup dropped into cold water forms hard, brittle threads, about 10 minutes. Brush the sides of the pan with a clean pastry brush dipped in water if any sugar crystals form on the sides of the pan.
Remove from heat and carefully add baking soda; stir quickly until foaming subsides and mixture turns golden. Pour into the prepared baking pan immediately. Cool until set, about 15 minutes. Break into bite-size chunks to serve.