BUTTER

This is really interesting for children to see. You just need to get double cream into a glass jar with a lid (fill it only to three quarters of the jar or so). Keep shaking it for 10 minutes: first you will see that the cream thickens and becomes like a really heavy paste; after a little bit longer the texture changes completely and you get a solid ball of butter floating in clear liquid.  Get rid of the liquid (it is bitter) and put the butter under tap water to get rid of any remaining bitterness. You can eat this immediately afterwards. The kids thought this was a 'science experiment' rather than cooking...