Crème fraîche is heavy cream that's been cultured and thickened by adding a fermenting agent and allowing it to sit at room temperature for several hours. Traditionally, crème fraîche has been made from unpasteurized cream that naturally contains the right bacteria to ferment it. In the United States, producers add fermenting agents to pasteurized cream.u003cbr/u003eu003cbr/u003eCrème fraîche tends to be thicker, richer, and less tangy than sour cream, though the two ingredients are made through somewhat similar processes.u003cbr/u003eu003cbr/u003eYou can make your own crème fraîche by adding a tablespoon of buttermilk to one cup of heavy cream and letting it sit, partially covered, on the counter for up to 24 hours until it's as thick as you like it. You can use a mason jar or a glass measuring cup. Or just buy your crème fraîche at the store.u003cbr/u003e