Full-fat Greek yogurt is both creamy in texture and tangy in flavor and, despite its name, actually contains less fat than créme fraîche, not only making it a potential substitution, but a healthier one at that (via Kitchenous). Of course, like sour cream, this makes Greek yogurt susceptible to curdling when subjected to high temperatures, so it’s best to hold off on adding it into a sauce, soup, or stew until the end of the cooking process, either over very low heat or no heat at all. This swap works incredibly well when replacing créme fraîche in a salad dressing, and can also be used as a substitution in dessert recipes, though A Couple Cooks notes that its lower fat content may affect the final texture of your treats.
Greek yogurt has become somewhat of a hot commodity in recent years, meaning that if you don’t already have a huge tub of it in your refrigerator, you can easily find it at the store. It is also another effortless replacement for créme fraîche that can be substituted in equal amounts.