Coarsely chop the chestnuts, leeks, fennel, and celery root. Melt the butter in a large pot and add the chestnuts and veggies. Sautée, stirring occasionally, until veggies are soft and beginning to look translucent. Add stock, bay leaves, and vanilla bean and simmer for 45 minutes or until everything is quite soft. Puree in batches until perfectly smooth; return to pot. Add wine and spices to taste.

Combine cream and egg yolks, slowly whisk in a bit of puree. Add back into remaining puree, whisking briskly. Take care not to overheat.

Garnish: Heat oil over medium-high flame. Add sage in batches; do not overcrowd. Cook for a few minutes, until it just starts to turn brown. Remove from oil and drain on paper towels. Store in airtight container for up to 2 days.

serving: Ladle soup into soup bowls. Draw flower petals with creme fraiche, arrange the fried sage to make the center of the flower, and add six drops of truffle oil to each bowl.