from lisa huang
Lisa says that when she was in preschool, they used to make butter as a class, each person giving the jar one shake. I had no idea you could make butter -- this is the best ever.
Put cream and salt in a jar. Seal tightly. I oversalted to begin with, but it ended up coming out perfectly. Shake a lot.
First, things start to solidify. The cream begins to get a little thicker, but stays white. Just at the point where you've decided it's not going to get any thicker, keep shaking, and the buttermilk will start to separate out. Take off the lid a lot and look to see where the butter's at, it's really cool to see it go through the stages. Things go from solid-like to sloshy, when the buttermilk saps out most of the salt you put in. Periodically pour off the buttermilk, and let the rest of it turn that lovely light yellow butter color. Keep shaking for a while (this is forty minutes or so -- share the labor!) and eventually you will have the best butter ever. Spread on whatever bread you have available, preferably fresh, but what the hell, just eat it plain if you have none.