After making this smooth, silky and most delicious concoction for so many years I have found out several things that make this recipe work every time. First of all, it is most important to use a glass jar. I tried this with plastic containers and it just doesn’t work: Definitely a chemistry thing. Secondly, by using more buttermilk than what is used in the original recipe from the 1800’s will give it a thicker consistency. And, finally, letting it stand at room temperature for 36 hours instead of less than the original recipe gives the mixture time to develop the necessary chemical reaction it needs to become thick. Once you refrigerate the mixture and it becomes cold the developing stops.
For each cup of heavy cream used mix in a scant ¼ cup of buttermilk. Pour heavy cream into a glass jar, such as a Mason jar, add the buttermilk and mix well. Cover the jar with a lid and let stand at room temperature in the coolest and darkest part of the kitchen for 36 hours. Refrigerate for 48 hours before using. The crème fraiche will last, refrigerated, for at least two weeks.
Crème Fraiche can be used in any recipe calling for sour cream. One of the advantages of using Crème Fraiche instead of sour cream in recipes that require cooking is the Crème Fraiche does not break. Plus the flavor is so much more delicious than sour cream.