Step 1Melt the butter in a large saucepan over low heat. Add the celery, onion and fennel; cover and cook until the vegetables are translucent, about 15 minutes.
Step 2Wrap the thyme sprigs, bay leaf and cloves in a piece of cheesecloth, tie with a piece of kitchen string and add to the vegetables with the chicken broth, chestnuts and brandy. Bring to a boil, reduce the heat and simmer, partially covered, until the chestnuts are very tender, about 45 minutes. Discard the cheesecloth bundle.
Step 3Puree the soup, in batches, using an immersion or regular blender. Return it to the cleaned pot, add the cream and pepper and reheat. Taste for seasoning.
Step 4Fold the thyme leaves into the whipped cream or creme fraiche. Garnish each cup with a dollop.