The next time you chop up a head of cos lettuce for salad, hang on to the very bottom. The "heart" can be placed in a pan of water and eventually sprout a whole new head of lettuce, ready to harvest, eat and repeat the process.
We've shown you how to do the same thing with spring onions (just save the bottoms,) and the process is similar with cos lettuce (often known as romaine lettuce in the US). Just leave a few inches from the bottom of the heart when you chop it up, and then put the hearts into about 1cm of water -- either nestled together in the same container or in separate, smaller ones like the cups shown above. Then, just wait a few days. Keep a little water in the bottom (change it out every day or so) and let them get some light, and you'll have fresh lettuce sprouting from the centre of the heart in no time.
You'll have to let it grow for a while before you get enough to harvest and start the process over again with, and you'll want to trim off the outer leaves of your starter heart, since they'll certainly turn brown and withered. If you want, you can even take the newly sprouted hearts and plant them right in the ground. Click the link below to read how the whole thing was done.