I have never made such a satisfying, delicious mess. Making the butter was easier than I thought possible. Storing the butter, on the other hand, was so much harder than I'd ever dreamed. But don't be scared! My monumental failure will help you succeed.
You will need one pint of the highest quality heavy whipping cream you can find. Fresh, local, organic, pull out all the stops.
And that's all. You'll also want a medium-sized mixing bowl and an electric mixer. You could do it by hand, I suppose, but I can't even imagine the biceps you'd need for a job like that.
It's a simple process. Pour the cream into your bowl, and start whipping. It quickly becomes whipped cream, and then it breaks into white-ish curds. And then, it turns golden, clumpy, and buttery. It begins to stick to the mixer and there...in the bottom of the bowl....buttermilk. The whole process takes about ten minutes. I stopped whipping every minute or so to look at what was happening and scrape the sides of the bowl. It was fascinating.
So you've got a bowl of butter and buttermilk. What now?
I can't emphasize this enough: GET CHEESECLOTH. Invest in it. Love it. Cherish it. Use it. Transfer the butter to the cloth and squeeze out the buttermilk. You can save the milk for use in later recipes. (Mine ended up in the sink, because I didn't have cheesecloth. I used a combination of my hands (oh-so messy) and a plastic bag (less messy) because I was a fool who didn't buy cheesecloth.)
Once you've squeezed out the buttermilk, you're going to get messy. Pick your storage container of choice. (Mason jar, tupperware, etc...basically anything with a lid that can be sealed tightly.) Open it. Dig in. Using your hands, pull out walnut-sized bits of butter and press them into your jar. The point here is to make sure there's no air in there. Once it's all packed in, top your butter with a layer of cold water, and put the lid on tightly. The water will keep out any extra air. To use your butter, simply pour the water off and put a fresh layer on when you're done.
The end. I think I've been clear and precise here, but comment with any questions you might have.