During the holiday time, it seems I use creme fraiche a lot. At times, it is hard to find in our local grocery stores, so I have started making my own. It is so easy to make, I don't know why I didn't do it sooner.
You need just two ingredients, heavy whipping cream and buttermilk or plain yogurt. That's it. Begin by heating the cream to about 105 degrees F. Transfer the warm cream to a bowl and add the buttermilk or plain yogurt. Cover the bowl with plastic wrap and let the mixture sit at room temperature from 24 to 36 hours. The cream is ready when it is thickened - it will look like mayonnaise or thick yogurt. The taste is slightly tangy with a nutty flavor. It will last 10 days in the fridge.
From Joy of Baking Blog
1 cup heavy whipping cream (cream with a 35-40% butterfat content)
1 tablespoon buttermilk or plain yogurt
1. In a medium saucepan, over low heat warm the cream to about 105 degrees F (40 degrees C). Remove from heat, transfer the cream to a bowl, and stir in the buttermilk or plain yogurt.
2. Let this mixture sit at room temperature, loosely covered with plastic wrap, until thickened (like mayonnaise or thick yogurt). This will take anywhere from 24 to 36 hours.
3. When ready, stir the cream and then cover and place in the refrigerator until well chilled (at least 8 hours, preferably overnight). Creme fraiche can be stored in the refrigerator for up to 10 days.
Makes 1 cup