Heat oil in large pot over medium; sauté onion 5-6 minutes until soft and translucent.
Add carrots, celery, and garlic; cook another 5 minutes until vegetables start softening and garlic is fragrant, stirring occasionally.
Add broth, thyme, salt, pepper, and bay leaves; boil, reduce heat to low, and simmer 20 minutes until vegetables are very tender.
Remove bay leaves; puree completely smooth with immersion blender, or carefully transfer to blender in batches.
Taste; adjust seasoning as needed. Serve hot with optional fresh herbs.