Bring a medium pot of water to a boil.
Set aside 12 bite-size cauliflower florets. Coarsely chop remaining cauliflower and set aside. Drop the 12 florets in boiling water and blanch for 2 minutes. Drain and set aside.
Heat oil in a medium saucepan over medium heat. Add onion and celery, and cook until soft, about 5 minutes. Add chopped cauliflower, broth, half-and-half, thyme, pepper, and nutmeg. Cover and simmer until cauliflower is tender. Puree the soup in a blender and return to the pot.
Stir in the cheese and salt until the cheese melts and the soup is heated through, 3 minutes. Serve topped with cauliflower florets.
Tip: For a vegetarian soup, use vegetable broth instead of chicken broth.