4 Tbs. unsalted butter
Melt the butter over medium heat in an eight-quart saucepan. Add the onion and cook until translucent. Add the celery and cook until the celery is soft, then add the parsnips and cook for another minute or two. Add the wine to deglaze saucepan and reduce until almost dry.
Pour in the chicken broth, using enough to cover the vegetables by one inch, and add the chopped thyme. Bring the ingredients to a boil, then lower the heat and simmer until the parsnips are soft. Add the cream and cook for another seven minutes at a low simmer.
Remove from heat and purée the mixture in a blender on a low setting, then strain through a chinois (fine mesh strainer). Serve with a drizzle of truffle oil atop the soup and salt and pepper to taste.