While its name translates as “fresh cream,” crème fraîche is almost the opposite of that: it’s heavy cream that’s been cultured or fermented, rendering it not fresh, but alluringly tangy. Crème fraîche’s closest American relative is sour cream, but crème fraîche is thicker (the best crème fraîche pulls from the tub like taffy), denser, silkier, and slightly sweeter. It can also do two things that sour cream can’t: it can handle heat without curdling, making it a terrific sauce thickener, and it can be whipped. In cooking, heavy cream is the best substitute for crème fraîche — you won’t get crème fraîche’s tang, but you won’t have any separation anxiety either. In baking, the best substitute is heavy cream, although sour cream will work in some recipes. But when you want the texture and slight sourness, crème fraîche is the choice. While it’s expensive and not always easy to find here, you can easily make a faux crème fraîche at home, you just have to plan ahead (page 491).