Heat oven to 400 deg F.

In a large roasting pan, toss cauliflower, onion slices and garlic with olive oil.

Roast at 400 deg F for 30 mins stirring half way through.

In large saucepan, combine roasted cauliflower mixture, chicken broth, 1 cup of water, bay leaf and thyme. Cover; bring to boil. Reduce heat; simmer covered for 20 mins.Discard bay leaf. Puree soup with stick blender, stir in half and half, salt and pepper; cook over medium heat until heated through.