Recently I bought a half-gallon of whipping cream and then didn't end up using it all before the expiration date, so I decided my children could learn to make butter. (We've done it before a few times, but it had been awhile.)
You're supposed to let the cream set out at room temperature for an hour or so, but I forgot that step... and I think that's why this next step ended up taking a lot longer than I remembered.
Anyway, fill a quart jar about half full of cream. It needs plenty of room to slosh. Make sure you close it tightly so it doesn't leak when you shake it.
And then just shake the livin' daylights out of it! Shake and shake and shake until you're tired of shaking... then pass it to the next person and let her shake awhile.
It will get to where you don't hear or feel it sloshing any more, and the jar looks like it's completely full. But you aren't done yet. Keep shaking!
After awhile (maybe 20 minutes? or probably less if you remember to let the cream set out for a bit before you start), all of a sudden, you will feel the sloshing come back and the white cream will "break apart" inside the jar. Then you're almost done. But not quite.
Shake it a little longer. You will notice “grains” of butter begin to form that look a little like foam. Continue to shake it until the grains clump together to form a ball of soft butter floating in buttermilk. Dump it in a bowl and drain the buttermilk off the butter. (It can be used for making biscuits or anything else you would use buttermilk for.) Now you need to rinse your butter. Add cool water and stir into the butter, draining off the milky water and adding fresh water until the water is clear. Continue to stir the butter until all the water is worked out of it. Add salt if you like. Spread on bread and enjoy!
If your family is used to eating margarine, keep in mind that real butter tastes very different.
My mother tells me that you can also make butter in a blender... but where's the fun in that?
Also, I haven't figured out yet if it's cheaper to just buy butter, or buy the cream and make my own. I wish I knew someone who has a cow!