I made myself a butter churn out of an old plastic peanut butter jar and a wooden spoon. I know many elementary school classes just put it in a jar and shake it, and apparently you can also just use a mixer.
After making my butter churn (with the help of an Xacto knife), I grated half a carrot and microwaved it for 45 seconds with 2 T skim milk and 1 T heavy cream (to make the yellow color, as described on page 30). Then I strained it and cooled it for about an hour. I poured the milk/cream mixture into my churn and then added enough heavy cream for it to be filled halfway (a little over a half cup).
I churned for about two hours (while watching Ace of Cakes), alternating twirling the spoon in my hands and stirring. Once it was finished, I rinsed it and salted it. The final step--eating it. It tasted like...butter!