Start your Thanksgiving dinner with this elegant soup, to highlight the flavors of fall. This recipe can easily be prepared in advance of the holiday meal. Indulge your guests with this velvety soup bursting with an earthy flavor of mushrooms.
In a large pot, melt the butter over medium flame; add the onion, leeks, and garlic, and sauté for 4 minutes until translucent. Toss the thyme into the pan, along with the mushrooms, season with salt and pepper. Cook, stirring, for 10 to 15 minutes, until the mushrooms give off their liquid. Remove about 1 cup of the mixture to save as a garnish for the soup.
Pour the stock into the pot and bring to a boil. Reduce the heat to medium-low and simmer, uncovered, for 15 minutes, stirring now and then. Remove from the heat and puree the soup until completely smooth, using a handheld or regular blender. Stir in the crema to make the soup even richer, and simmer gently for 5 minutes. Taste for salt and pepper.
Ladle the soup into soup bowls; garnish each serving with a bit of the reserved mushrooms and a sprinkle of chopped chives.
If you cannot find fresh shiitake mushrooms, use a different wild mushroom, like chanterelles or morels.