A Pioneer Sampler: The Daily Life of a Pioneer Family in 1840, Barbara Greenwood (p. 82-83).
As a part of her history studies, lovely lady made her own butter yesterday. She was surprised at how easy and how good it was. "It tastes like real butter!"
To make butter in a jar: Pour a cup of whipping cream into a smallish clean glass jar and shake vigorously until it solidifies into butter. If your arms get tired, enlist the help of your mom, your little brother or a friend. Once the butter is in solid lumps, pour off the buttermilk into a separate container and save to drink or to use in place of milk in a recipe. In a bowl, press the butter into a solid lump to squeeze out the remaining buttermilk and rinse the butter in running water. Mix in a little salt if you wish. Put your butter in a small dish, spread some on a piece of bread and eat. Delicious!
Step-by-step directions with pictures.
It's science! Try this butter-making experiment from Science Kids at Home.
Read about making butter in your mixer at Cooking for Engineers.