We spent the last 45 minutes ranting to ourselves over a cookbook that would specify low-fat crème fraîche. Not that some - perhaps many - foods can't be made with less fat. But this is a little like asking for low-fat foie gras or cooked sushi.

If you take away the essential elements of something, what do you have left? At some point, if it doesn't look like a duck and doesn't quack like a duck, it isn't a duck.

And it is especially problematic with crème fraîche, which is very hard to obtain in this country and very expensive when you find it. So most people in this country make a close approximation, which can only be made with full-fat cream. And, given the general difficulty of finding crème fraîche in stores, we do not believe that there is 1 chance in 3 million of finding low-fat crème fraîche at your corner market.

So where does that leave you? (A little bit sorry that you asked this question in the first place, no doubt.) But of course you can use low-fat sour cream or yogurt in that recipe, although the sour cream would be our choice. And you're right, one of the great advantages of crème fraîche is that it will not curdle when boiled, while sour cream and yogurt will. So keep the temperature low enough.

You can also make a low-fat crème fraîche substitute, although it's not as close to the real thing as low-fat sour cream. Mix 1/2 cup of fat-free sour cream and 1/2 cup of 1% milk and 1 teaspoon of sugar. Cover and let stand out for 8 hours to thicken. Refrigerate for 4 hours before using. Cover and refrigerate up to 2 weeks.

Then buy a new cookbook.