- 1 cup heavy cream (not ultra-pasteurized)
- 1 cup sour cream
- Whisk the heavy cream and sour cream together in a bowl. Cover loosely with plastic wrap and let stand in the kitchen or other reasonably warm spot overnight, or until thickened. In cold weather this may take as long as 24 hours.
- Cover and refrigerate for at least 4 hours, after which the crème fraîche will be quite thick. The tart flavor will continue to develop as the crème fraîche sits in the refrigerator.