In a 4½-quart pot over medium-high heat, combine oil, onion, garlic and sweet potatoes. Cover and cook, stirring occasionally, 10 min. Add salt, lime juice, honey, cumin, chipotle pepper and 3 cups broth and bring to a simmer; cover and cook until very soft, 18 to 20 min.
Remove from heat. Add 1 cup broth and milk. Use an immersion blender to purée the soup. (Alternately, in batches, purée soup in blender, holding lid on with a towel while blending.) Serve with cheese.
A mildly spicy, sweet and savory meal, chipotle sweet potato soup with queso blanco is an easy dinner to get on the table for a cozy night in.