Using a large pot, heat the olive oil over medium-high heat. Add the mushrooms, onions, and garlic and season with salt and pepper. Cook until the onions are translucent. Add the ground beef, cooking until browned. Stir in the smoked paprika. Add the beef stock and noodles. Stir and cover with a lid. Simmer for 15 minutes. Mix the cornstarch with enough water to make a slurry. Reduce the heat, add the slurry, and stir constantly until thickened. Add the sour cream and stir. Add salt and pepper to taste. Garnish with parsley.