Add the butter to a large soup pot over medium-high heat. Once the butter melts and becomes foamy, add the garlic, onions and ginger and saute until tender and fragrant, 3 to 4 minutes. Season with salt and pepper. Add the chipotle pepper and saute for 1 minute longer while breaking it up with a wooden spoon. Add the chicken broth, apple cider and sweet potatoes. Bring to a simmer and cook until the sweet potatoes are tender, about 20 minutes.
Puree the soup using an immersion blender until smooth and velvety. Finish by stirring in the heavy cream. Top each bowl with sour cream if using.