Combine all ingredients (except lime, scallion and sour cream) in slow cooker. Cook on high for about 6 hours or until beans are very soft. Turn off slow cooker and using an immersion blender, blend soup until creamy. Add lime juice. Adjust salt seasoning to taste. Add optional garnishes of scallions and/or sour cream.
Recipe by https://veggingonthemountain.com/ at https://veggingonthemountain.com/2015/01/slow-cooker-black-bean-soup/