Is there a substitute for creme fraiche?
It depends on the recipe. In some cases, you can use sour cream, which has a similar consistency. But sour cream is tangier and lacks the creaminess of true creme fraiche. However, it’s easy to make a version of creme fraiche at home. There are a couple of ways to do it. You can mix 1 to 2 tablespoons of buttermilk into 1 to 2 cups of heavy cream and heat it over low heat in a saucepan until it thickens. Or you can mix equal amounts of sour cream and heavy cream – say, 1/2 cup each – and let it stand at room temperature until it is thickened.
Depending on how warm your kitchen is, that might take anywhere from several hours to 24 hours. But if you save a couple of tablespoons and add it to the next batch, it will often thicken faster.