Is there a respectible exchange I can make for creme fraiche in a pasta recipe?
Sour cream is probably the closest. If it's for a sauce, you could cut it with a little heavy cream. It's easy to make your own creme fraiche. Lots of different recipes to be found, but my favorite is equal parts heavy cream and sour cream, shaken in a lidded jar, let sit at room temp 12 hours or overnight, then refrigerate until ready to use.
Thanks for the info on how to make it--will try that later. Tongith, though, I have a craving for a pasta sauce recipe that includes it, so will have to go with the sour cream/heavy cream for now! Thanks again, Mrslarkin!
If you have more than a day, but can't find crème fraiche at the market you can make it by adding a small amount of buttermilk to heavy cream and let thicken at room temperature. Sour cream is fermented with the same bacteria, but has slightly less fat than crème fraiche so cooking can curdle it. If you're adding off heat you should be fine, or you can try stabilizing with some starch and adding slowly. Some of the Mexican and Central American crema have enough fat to withstand cooking--I know the crema Salvadoreña I buy does.
Another direction you could go in, with a slightly different flavor profile, which won't curdle is mascarpone. mmm...mascarpone.
Sour cream may curdle if you heat it too much. Cream fraiche doesn't. I don't know why you want to make a dish when you don't have a main ingredient. Perhaps if you have regular cream, you can reduce it by half to thicken it. Add a bit of sour cream to the dish off heat, afterward, to give tangy flavor.
Depending what you want, Vermont Butter and Cheese makes a wonderful fat-free fromage blanc that I use in place of creme fraiche.
You can make it out of cashews. http://veganepicurean.blogspot.com/2010/07/cashew-creme-fraiche.html
I've never had a problem using sour cream, and as pointed out above, it is much lower in fat.