2 c heavy cream (not ultra pasteurized)
3 T cultured buttermilk
Warm the cream in a glass bowl over simmering water just until warm, not hot. Turn off heat. Stir in buttermilk. Pour the cream in a glass jar, put on the lid, and let it sit at room temperature in a warm place for 24 hours. Stir the cream occasionally (every 6 hours). At the end of 24 hours, stir it well, then put the lid back on and let it sit in the refrigerator for 24 hours. Then the creme fraiche is done. Use the creme fraiche within 7 to 10 days.
Creme fraiche can be used in place of sour cream in all recipes. It can be whipped (sour cream cannot be) and it will not curdle in hot dishes as sour cream does.