Peanut brittle is a hard, glassy confection of caramelised sugar set around roasted peanuts. Sugar (usually with corn syrup and a little water) is boiled to the hard-crack stage, the nuts and often a knob of butter are stirred in, a pinch of baking soda is added to aerate it, and the molten mass is poured out thin, cooled and snapped into shards — deep amber, sweet and buttery, with a toasty roasted-peanut crunch that shatters cleanly between the teeth.