In a dutch oven, melt 1 tablespoon butter over medium heat. Add onion and celery and cook, stirring occasionally, for 5-6 minutes until onions are translucent.
Add garlic and thyme, then stir well.
Add carrots, water and broth to a large dutch oven and bring to a boil. Reduce the heat to a simmer and cook 25-30 minutes until carrots are tender.
Use an immersion blender to puree the soup, or blend in a food processor or blender in batches.