In a large soup pot, add the olive oil and heat over medium heat. Add the onions and cook for 3-4 minutes until onions are soft. Stir frequently. Add the cauliflower and potato, thyme, basil or tarragon, salt, pepper, and garlic. Cook for another 4 minutes, stirring often to insure even cooking. Turn down heat, add the broth; cook for 20 minutes or until cauliflower and potatoes are tender.