Homemade Creme Fraiche
In a small bowl, thin the sour cream with a little cream. Combine the remaining cream with the sour cream mixture in a small saucepan. Gently heat to no more than 90 degrees F., to take off the chill. 2. Pour into a clean glass jar cover loosely, and let thicken at room temperature for 4 to 12 hours. (It will probably take about 4 hours to thicken in a warm room).
Cover the jar tightly and refrigerate.