Prepare a screw top jar. It must be clean, dry, and not smell like it's previous contents. (Peanut butter jars work great, as well as baby food jars for smaller portions).
Pour the cream into the jar, and put the lid on. You will need to leave the jar about half empty to have space to shake, so adjust the amount of cream accordingly.
Shake the jar vigorously. After a bit, it will coat the sides of the jar, then become whipped cream. Keep shaking - it will start to separate. Its done when it is totally separated into butter and buttermilk.
NOTE: I stopped every minute to open the jar and take a picture (and let my arm rest :-) ) and it took 7 minutes of shaking. After several reviews, I thought that I'd mention that it takes some people longer - even 20 or 30 minutes - but it is still worth the time to make :D .
Pour the buttermilk into a separate container, and enjoy!
A great project for school kids is to use the buttermilk to make biscuits or bread, and then eat it with the butter. While it is very soft at first, it gets rather hard as you store it in the fridge, and will need to soften if you plan to use it as a spread. (If you don't eat it all right away!).
While researching cheese making I discovered that the resulting butter milk is 'old fashioned' and purchased buttermilk is thicker as it is cultured in a process similar to yogurt. (Someone mentioned this in a review as well.) I have used it with great success in a few recipes without knowing that there was a difference.
