combine cultured buttermilk (it is very important that it has the culture in it to keep from going bad. if you buy buttermilk from the store it will say it on the carton) and cream in a clean jar and seal it with a lid.

the hard part is over!

let it sit in a warm-ish place for 8-12 hours or overnight.

after that time has elapsed, give the jar a shake and open it up. check to make sure it has thickened and refrigerate. use it within 7-10 days :)

side note: I made this for the first time a couple months ago and loved it. I had dinner at a friend's house a week later and used some store bought sour cream and actually thought something was wrong with it because of how different it tasted! it was brand new, not expired, and nobody else thought it tasted "off." this is essentially a warning: this stuff is so simple and so much better than regular sour cream that you will probably never be able to go back. enjoy!