Sweet Potato and Chipotle Soup

INGREDIENTS

• 2 tablespoons olive oil
• 1 medium white onion, chopped
• Coarse salt and ground pepper
• 2 teaspoons ground cumin
• 2 garlic cloves, minced
• 4 medium sweet potatoes (2 pounds total), peeled and cut
• 1/2 to 1 chipotle chile in adobo, chopped
• 7 cups low-sodium chicken broth
• Sour cream, for serving
• Toasted flour tortilla wedges, for serving (optional)