What can I substitute for créme fraiche?

If you can't find créme fraiche at the store, make your own: combine 1 cup of heavy cream with 3 tablespoons of buttermilk or 1/2 cup of sour cream; cover the container and let it sit overnight. In the morning you will have thick, slightly tangy, buttery créme fraiche.

Recipe: Rustic Pear Tarts with Créme Fraiche