Sprinkle 3/4 tsp. salt, pepper and 1 tsp. paprika all over beef. Warm oil in a large skillet over medium-high heat. Cook beef, stirring occasionally, until browned on all sides, about 8 minutes. Transfer meat to a slow cooker.
Add mushrooms, shallots and remaining 1 tsp. paprika to skillet; season with salt and cook for 3 minutes, stirring often. Combine beef broth and sour cream, pour into pan with mushrooms and shallots, and cook for 2 minutes, scraping up any browned bits from bottom of pan. Pour mixture over beef in slow cooker, cover and cook on low until beef is tender, 6 hours. If desired, sprinkle with chopped fresh dill or parsley before serving.