1. Microwave onions, paprika, tomato paste, oil, garlic, and caraway seeds in bowl, stirring occasionally, until onions are softened, about 5 minutes; transfer to slow cooker.
2. Stir broth, soy sauce, tapioca, and bay leaves into slow cooker. Season beef with salt and pepper and nestle into slow cooker. Cover and cook until beef is tender, 9 to 11 hours on low or 5 to 7 hours on high.
3. Let stew settle for 5 minutes, then remove fat from surface using large spoon. Discard bay leaves. In bowl, combine 1 cup hot stew liquid with sour cream (to temper), then stir mixture into stew. (Adjust stew consistency with additional hot broth as needed.) Stir in parsley, season with salt and pepper to taste, and serve.
Recipe from America's Test Kitchen book: Slow Cooker Revolution.