How to Make Crème Fraîche   [Photographs: Sue Veed]  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,
science-project-style fun.  True to its name, 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 Mak