In a large skillet, heat the olive oil over medium-high heat. Add the diced onion and sauté for 3-4 minutes until softened.
Add the minced garlic and sliced mushrooms to the skillet. Cook for an additional 5-7 minutes until the mushrooms are browned and their moisture evaporates.
In the slow cooker, combine the sautéed onion, garlic, and mushroom mixture with the beef chuck roast.
Stir in the beef broth, Worcestershire sauce, dried thyme, paprika, and season with salt and pepper to taste.
Cover the slow cooker and cook on low for 6 hours, or until the beef is tender.
About 30 minutes before serving, whisk together the sour cream and flour in a small bowl until smooth. Stir this mixture into the slow cooker and let it cook for an additional 30 minutes to thicken.
Serve hot over cooked egg noodles or rice. Garnish with chopped parsley if desired.