Can Creme Fraiche be substituted for Heavy Cream in a Cream Sauce?

Actually I would disagree to some extent with the other two answers - I think you can use creme fraiche instead.

I agree with MStodd that it will certainly give a different flavour and texture to the sauce, but if you're just looking for a healthier base to a pasta sauce, I'd say it's fine to substitute. Also as daniel mentions, you have to be careful not to overheat it (although the same is true of cream), as it will curdle.

In my experience, creme fraiche is great to make a very quick and easy pasta sauce. Put it in right at the end of cooking, once everything else is properly cooked and just heat enough so it is warmed through.

It comes down to whether you are wanting to achieve the same flavours though - if you are, maybe you could try what I would call single cream (not sure what it would be called in the US), and thicken the sauce with a bit of cornflour mixed with cold water.

Not a whole quart of it. That much creme fraiche will totally throw off the flavor and texture of the sauce. Do you actually have a quart of it lying around, or are you just wondering?

In regards to creme fraiche and curdling -- actually creme fraiche is much more stable and less likely to curdle than cream or milk. It is made to be used in sauces for that reason. Yes it does have a tangy flavor that is different than cream. It is my experience to actually use both. For example in a recipe that calls for 1 cup of creme. I suggest 3/4 cup of cream and 1/4 cup to 1/8 cup of creme fraiche. Why include creme fraiche - it is less likely to curdle so adds stability to the sauce. It also adds more viscosity to the sauce than just cream. Finally, creme fraiche that is a "homemade" version versus one made in a specialty dairy are not the same product. The one made in a specialty dairy such as vermont creamery is much more stable and better because it used milk and cream to make creme fraiche versus trying to take cream and buttermilk to recreate or engineer it in a kitchen. Here is a link www.vermontcreamery.com/creme-fraiche-1 . I do not work for vermont creamery or any other manufacturer of such products.

Not really, no. I mean you could but it's liable to curdle somewhat, and will be significantly thicker and less velvety than a comparable sauce made with cream. In addition, the flavour of creme fraiche is very different from heavy cream; it is tangier and more buttery.