Once you have cultured buttermilk, making creme fraiche is a snap.
One pint heavy cream
3 Tablespoons cultured buttermilk
Put the cream into a clean jar. Stir in the buttermilk. Rest the lid on top of the jar. Let it sit out at room temperature for 16-24 hours, or until thickened. Then store in the refrigerator for up a week. It really is that easy.
You can use as you would sour cream. Or try a dollop a top a slice of fruit pie. Or on a scone.