We had a milk cow when I was growing up in southern California. My mother skimmed the cream off of the milk from our cow every day to put in a gallon jar, which she left on the counter until we had enough to churn. Since Southern California was never cold at the time, the cream would sour.
Once every seven to ten days, we would churn it. She had a gallon churn with a paddle that you turned. Each of us three younger ones were supposed to take turns churning, but we always got into arguments about one not turning fast enough, etc., so our mother put the churn away and gave each of us a quart jar that we had to shake until the cream separated from the milk. We never argued while shaking the jar, but instead had a great time talking, etc., until the cream separated from the milk.
The butter was delicious. For years after I married and moved to Virginia with my husband, I looked for sour cream butter everywhere, but never could find any.
We went to Pennsylvania many years ago to check out the state college there, but it didn't cross my mind until we got home that we could probably have bought sour cream butter from the Quakers. I imagine they even have restrictions from selling now.