There's something very satisfying about making your own butter at home, with the added benefit that you get some buttermilk too.
Pour the cream into a large bowl and whizz with an electric whisk. After about 2 minutes, it becomes whipped cream. But you need to keep on going until it breaks down completely - first of all it will look a bit like scrambled eggs, and shortly after that the fat and the liquid will begin to separate. The whole process takes 5-10 minutes.
Strain the solids from the buttermilk and place onto a piece of muslin cloth (cheesecloth). Tie the four corners together and hang it over the bowl of buttermilk. When liquid has stopped dripping from the bag, squeeze it gently to extract as much buttermilk as you can. Now untie the bag, sprinkle salt over the butter and work it in with a spoon.
At this point, you might want to 'wash' the butter - this removes every last trace of buttermilk and will make your butter last longer. Basically, put the butter into a bowl of iced water and press it/squeeze it with your fingers or a spatula. Any ejected buttermilk will make the water cloudy. You may need to change the water 2 or 3 times until the water stays clear.
You might want to experiment with other flavourings such as chilli, cumin, parsley etc.
Put your butter into a ceramic container, and smooth the top flat with a palette knife. Alternatively, you might want to pat it into a rectangular block with a couple of spatulas, or roll it into a log and wrap it in greaseproof paper. That's it! You've made delicious butter, and have a useful jar of buttermilk too.