In a large skillet, heat 2 tablespoons of the olive oil until shimmering. Add the mushrooms and cook over moderately high heat until softened, about 3 minutes. Season the mushrooms with salt and pepper and cook for 1 minute longer. Transfer the mushrooms to a bowl.
Generously season the steak with salt and pepper. Toss the steak with the flour until evenly coated; gently tap off the excess. Heat the remaining 2 tablespoons of olive oil in the skillet. Add the steak slices, without touching, and cook until richly browned, about 5 minutes. Transfer the steak to the bowl with the mushrooms. Add the wine to the skillet and stir to scrape up the browned bits from the bottom of the skillet. Add the wine to the mushrooms and steak.
In the same skillet, melt the butter until bubbling. Add the onion and cook until softened, about 3 minutes. Season with salt and pepper. Add the garlic and cook for 1 minute. Return the contents of the bowl to the skillet. Stir in the stock and Worcestershire sauce and simmer over moderate heat until the pan juices thicken slightly, about 7 minutes. Remove from the heat and stir in the sour cream, thyme and parsley. Season the stroganoff with salt and pepper and serve over fettuccine or egg noodles.