When you urinate into a partner's anal cavity, and proceed to use either your genitals or an appropriate tool to stir the liquids inside much like a traditional "churning" motion.
I had to grabmy boy Eric the other day and assert authority by giving him the oldAmish Moon Butter.
The act of peeing into an amish person's ass and then churning it with your cock.
Michael: "Dude i went to the amish market and met this girl."
Rupert: "Oh yeah what was she like, what did yall do?"
Michael: "Oh yea we made some amish moon butter."