Cinder toffee

Honeycomb toffee, honeycomb candy, sponge toffee, cinder toffee, seafoam, or hokey pokey is a sugary toffee with a light, rigid, sponge-like texture. Its main ingredients are typically brown sugar and baking soda, sometimes with an acid such as vinegar. The baking soda and acid react to form carbon dioxide which is trapped in the highly viscous mixture. When acid is not used, thermal decomposition of the baking soda releases carbon dioxide. The sponge-like structure is formed while the sugar is liquid, then the toffee sets hard. The candy goes by a variety of names and regional variants. Owing to its relatively simple recipe and quick preparation time, in some regions it is often made at home, and is a popular recipe for children. It is also made commercially and sold in small blocks, or covered in chocolate, a popular example being the Crunchie bar of Britain and Canada, or the Violet Crumble of Australia. Honeycomb toffee is known by a wide variety of names including:

Source: Wikipedia