I had some whipping cream leftover in the fridge so it was the perfect time to give it a shot. All you need is cream (30% or more), a jar with a tight-fitting lid, a piece of cheesecloth and some salt.
Pour the cream into a jar with enough headspace to allow the cream/butter to move around.
Then you shake the jar (a lot). At first you'll hear the liquid sloshing around, then it'll sound like there are chunks flying around in there, and then nothing. Don't worry though, it means that you've made whipped cream. Just keep shaking...and shaking...and shaking. Have you ever seen the infomercial for the shake weight stick thing? They exercise while shaking this stick? Well, whoever invented that must have made homemade butter. It's a great arm workout!
At some point when you're starting to wonder if you'll be a failure at making butter you suddenly hear something in the jar. Could it be? Did it work? Yup, there's something rolling around in there now and it's making a a clunking sound and there's some liquid sloshing around again.
At this point, cover the jar with a cheesecloth and drain out the buttermilk (use the buttermilk for pancakes!). That's not it though, the butter needs to be 'cleaned'. Run some cold water into the jar and strain out a number of times until the liquid being drained out becomes clear. It's important to remove all of the buttermilk from the butter to prevent spoilage.
To be extra sure that there isn't any buttermilk left spread the butter onto a cutting board and absorb any remaining liquid with a paper towel. Keep moving the butter around and blotting it until it seems to be pretty dry (only takes a couple of minutes).