- Heat the oil and butter in a heavy pot over low heat until butter is melted and foaming, about 1 minute. Sauté the leeks and celery for 10 minutes or until leeks are soft.
- Add the stock and cauliflower florets and bring to a boil. Reduce heat and simmer until cauliflower is tender, about 15 minutes.
- Puree the mixture with an immersion blender, adding the half in half in increments. For an extra creamy soup, strain through a fine sieve or chinois.
- Chill until ready to serve and garnish with a ½ teaspoon of white truffle oil and a cheese crisp.