Why It WorksMaking crème fraîche at home is an easy and cost-effective alternative to specialty store-bought versions.The bacterial cultures in buttermilk and yogurt thicken and acidify the cream, while also preventing bad bacteria from taking over.Adjusting the amount of buttermilk or yogurt and amount of time left at room temperature will determine the consistency of the finished product.Finally, I found a plus side to the summer heat. It's currently sitting on my windowsill.For all the hubbub made over crème fraîche—gourmet markets charge an arm and a leg for this creamier, milder cousin to sour cream, and chefs and television cooks mostly treat it as a specialty item, often naming a substitute for folks who can't find or afford it—it's shockingly easy to make at home, and half as expensive. Not to mention it's science-project-style fun.As its name suggests, crème fraîche has roots in France. Historically, it was fresh cow's cream left out of refrigeration to become sour. The natura...