I usually edit this method for making creme fraiche that I got from June Jacobs a few years ago, but I'll post the entire thing for you to look thru. I've been making hers for a long time and it's just wonderful.
CREME FRAICHE - HOW TO MAKE
June Jacobs
2 cups whipping (heavy) cream preferably NOT ultra-pasteurized
1/4 cup buttermilk -- room temperature
1. Warm cream in heavy small saucepan to lukewarm (85 degrees F). Remove from heat and mix in buttermilk. Put the mixture into a clean glass jar (that has a tight-fitting lid), Leave the jar open and cover with a piece of waxed paper fastened with a rubber band. Let it stand in a warm draft-free area until slightly thickened, 24 to 48 hours, depending on temperature of room.
2. When the cream has "clotted," remove the paper and replace it with the lid. Refrigerate until ready to use.
Teacher's Tip Stored in this manner, the Crème Fraîche should keep until you've used it up (and made more!) Like fine cheese, it may develop a "skin", but you can remove it and use what's underneath.
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Jean's notes:
Well, murphy's law - my heavy cream WAS ultra-pastuerized and the only buttermilk on the shelves around here was/is reduced fat/1 1/2% milkfat/50%less fat than whole milk!!!
Decided to go with it and see what would result - oh my, it is delicious, creamy, beautiful creme fraiche. I left it 30 hours.
Now, I have to decide what to use it for - any suggestions? If nothing else, I could use it in my mashed tatoes Thanksgiving day.
June, how long will this keep? Any idea?
June - Wow, that is GREAT news! and besides, it WHIPS!!! so when you want that great tang on a strawberry shortcake, you can have it fluffy!
As well, it doesn't break if it gets boiled the way sour ceram does, so it's great for finishing sauces.
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I know these are just kind of mish mash notes, but you get the pix.