Melt butter in large heavy kettle. Add onion and cook, stirring often, 10 minutes. Add meat, paprika, and 1 teaspoons salt and cook, stirring, until meat loses its red color. Add green pepper, tomato sauce, bouillon cubes and 1 cup water. Cover and simmer 20 minutes. Add potatoes and heat. Stir in sour cream. Add more salt if necassary.