Fresh chestnuts are a seasonal delicacy perfect in fall soups and our version is simplicity itself highlighting the delicately sweet, nutty chestnuts.
In a large pot over medium heat melt butter. Add onions, carrots, and celery and cook 5-7 minutes until onions are translucent and vegetables are soft.
Add whole garlic cloves and chestnuts and stir. Cook 3 more minutes then add marsala wine and cook 5 more minutes until the alcohol has burned off. Add chicken stock and thyme sprig and bring to a simmer. Cover and let simmer on low for an hour until chestnuts are soft.
Remove thyme sprig. Working in batches, blend the soup with the heavy cream and half of the truffle salt.
Whisk together the creme fraiche and the remaining truffle salt.
To serve, ladle the soup into bowls and top with the truffle creme fraiche and the crispy onions.