Add yogurt/buttermilk mix to creme fraiche?
I have an 8-ounce container of creme fraiche and some italian plums that I want to use to make Annie Somerville's recipe (from Fields of Greens) for Nectarine-Almond Streusel Coffee Cake. Problem is that she calls for 1 1/2 cups. I do have plenty of yogurt and some buttermilk. Can I make up the difference with one of those?