Melt butter over medium heat in a 3 or 4 quart saucepan. Add bacon and saute for another couple of minutes or until the bacon has rendered some of its fat. Add the onion, cover and cook for about 10 minutes or until onion is translucent. Check the onion every now and then to make sure it is not burning. While the onion is cooking, dice the sweet potato. When the onion is translucent, remove the cover and stir in the sweet potato, spices and broth. Cover and simmer for 20 minutes or until tender.
Transfer soup to a blender or food processor. Add the tomato paste and peanut butter and puree until smooth. Season with about 1/2 teaspoon salt and 1/4 teaspoon pepper. You can make the soup up to this point 2 to 3 days in advance. Reheat, stirring on occasion, until soup is heated through and garnish each portion with sour cream and chives.