In a blender, puree 1 cup of the beans with 1 cup of broth and reserve. Cook onion, pepper, garlic, and sausage in oil in a 3-qt. saucepan over medium heat until vegetables are softened and sausage is browned, about 10 minutes. Stir in bean puree, remaining beans and broth, and tomato paste. Bring to a simmer and cook, covered, 15 minutes. Meanwhile, steam sweet potatoes over boiling water until tender, about 10 minutes. Stir sweet potatoes, hot sauce, and salt and pepper to taste into soup. Serve garnished with pumpkin seeds.