The Cambridge Science Centre at Cambridge University is located close to the serene Cam River, where punting is a popular form of recreation. Punting is an athletic activity and punters there are traditionally fueled by Chelsea buns, a type of sweet roll. Specifically, they’re fond of the Chelsea rolls made by a particular bakery and restaurant called Fitzbillies.
To promote their activities, the staff of the Science Centre decided to propel a punt down the river using a rocket instead of oars. The rocket itself would be powered by Fitzbillies buns. They made this engineering miracle work by freezing the buns into a solid block, then blowing nitrous oxide through a hole bored through the center of the block. This produced gas, which produced propulsive force. You can see a video of the successful launch at BBC News.