Vt. butter and cheese fat free fromage blanc.

I make it in my yogurt maker, and always have it on hand because there is so much you can do with it:
http://wp.me/p27pPl-il

Sour cream!

I've made this one many times - 2 parts cream to 1 part buttermilk. Stir often and let sit out for 12-24 hours until it's the consistency that you want. http://dashandbella.blogspot.com/2012/05/if-youre-in-mood.html

You could also sub in sour cream or plain yogurt.

It's usually sold in the refrigerated cheese section (not dairy aisle) of most markets. Sour cream would be a good substitute.

Make you own. I've never purchased it. It's a cup of heavy creme..and a tablespoon or buttermilk. Left out overnight on the counter top. http://www.seriouseats.com/recipes/2011/02/how-to-make-creme-fraiche-in-1-easy-step.html