I have been on a quest to modernize this German mushroom, leek and cheese soup for some time. It's usually made with a laughing cow sort of cheese that remains in the soup as little fatty bits because it does not quite melt. It's often thickened with flour and while I admit that it is good, it is also very heavy. I wanted the richness but I also wanted lots of mushrooms and more healthy and hearty ingredients. Adding the creme fraiche as a topping adds the creaminess and the cold butter yum which is far better than a processed cheese. But because the creme is on top a little goes a long way. Spring is here but I had to scrape the windows on my car this morning and this soup sounds perfect to me right now.