Combine carrots, chicken broth, and onion in a large pot. Add enough water to cover the ingredients. Add garlic, thyme, tarragon, grated ginger, and ground nutmeg.

Bring to a boil, then reduce heat to medium-low, cover, and simmer until the carrots are very tender, 40 to 50 minutes.

Remove from heat and carefully puree the soup with an immersion blender until smooth (or cool slightly and blend in batches).

Return to medium heat and cook until warmed through, about 5 minutes. Stir in the cream and serve.