Rachael Ann has devised a recipe for a tasty demonstration of the rock cycle.

The ingredients list and step-by-step instructions illustrate how the rock cycle can be explained using chocolate. First, pupils should decide what each chocolate symbolises: Lion bars are sedimentary; marble-effect chocolate is metamorphic; and Crunchies are igneous.

You can then get practical: grating chocolate represents weathering; applying pressure with utensils portrays sediment becoming rock; heating with a Bunsen burner shows how rock becomes metamorphic. Best of all, you and your pupils can always eat the experiment afterwards.