Heat oil in a large soup pot. Add garlic, celery and onion. Cook until vegetables have begun to soften and onion turns translucent, 3 to 4 minutes. Stir in butternut squash, thyme, chicken broth, salt and pepper. Bring to a boil, reduce heat and simmer until squash is fork-tender, about 30 minutes. Use an immersion blender to purée soup or you can let the soup cool slightly and carefully purée in batches in an upright blender. This recipe is also good made with sweet potatoes.