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 naturally occurring bacteria cultures would not only prevent it from spoiling, but would work to thicken and acidify the cream.
Since today, our dairy is pasteurized (if not ultra-pasteurized), we have to introduce outside lactic culture to make crème fraiche. Lucky for us, two inexpensive dairy-section neighbors have just what we need: buttermilk and yogurt.
How to Make It
To make a batch at home, all you do: add a small amount (1 to 2 tablespoons) of buttermilk or yogurt to a few cups of heavy cream, and let the mixture sit out in a clear jar or plastic container in a warm place for 12 to 24 hours. (I've read you should leave it uncovered, but—worried about bugs, dust and the like—I left the lid ajar for a few minutes, then sealed it, and was successful.) Within the day, the cream will have transformed to a thicker, tangier and more spoonable version of itself. Then just store it in the fridge, where it will continue to mature.
Even though some recipes recommend kickstarting the process by heating the cream mixture to take off the refrigerator chill, I found that using cold cream actually worked better. It made for a thicker, creamier result. Plus, after 12 to 24 hours at room temperature, the short amount of time you save by preheating the mixture is not that significant anyway over the long run.
Just as every brand of store-bought crème fraîche tastes different, yours will vary slightly depending on the flavor of your milk or yogurt, the butterfat content you can find, and how long you let it become sour. If you like a looser, runnier consistency, check your crème after 12 hours. I've left some batches as long as 36, especially when using yogurt, which I find produces a thinner version. Just keep in mind that the mixture will continue to thicken once you place it in the fridge.
Notes on Shopping
When choosing ingredients, try to find pasteurized* (as opposed to ultra-pasteurized) heavy cream, yogurt and buttermilk. I used a locally produced cream and a full-fat plain yogurt from Ronnybrook. I could only find 1 percent buttermilk in the markets near me (which I was worried would be too diluted), but it worked swimmingly.
Look out for wording on packaging! I've read that ultra-pasteurized cream takes longer to sour, but I haven't actually tried it myself. Have any of you?
Your crème will keep for around 7 to 10 days, plenty of time for you to dream up some fun ways to use it! Besides spooning some over fresh fruit, pancakes, cobblers or pies, you can use it in savory ways, too. Stir a little into pan sauces, soups or mashed potatoes—it tolerates heat better than milk or cream, and adds a richness and nutty flavor—or mix with lemon and herbs to serve with fish fillets. My favorite use to date: stirring it in to scrambled eggs before cooking. Simply out of this world.
There'll be plenty of buttermilk left over, too (which is partly why making your own pays off).