This is really easy to make. I make it myself because I can't buy organic creme fraiche and I also know that is it live and full of goodness.
Take 250g of double cream and put it in a jar. Add a tablespoonful or so of live cultured buttermilk (most supermarkets will have this). Stir through and leave in a warm spot for about 24 hours. There - creme fraiche! I just put mine into one of my kitchen cupboards the night before I want to use it and just like magic, the next evening it is set and ready.
A spoonful of creme fraiche is just the thing to finish off soups.