Pat sliced beef strips dry with paper towels. Season evenly with garlic powder, onion powder, 1/2 tsp kosher salt, and 1/2 tsp black pepper.
Heat olive oil and 1 tablespoon of butter in a large heavy Dutch oven or deep skillet over high heat. Add beef strips in a single layer and sear undisturbed for 2 minutes to develop deep golden crust. Stir and sear for 1 more minute until browned. Transfer seared beef and juices to a plate and set aside.
Reduce heat to medium. Melt remaining 2 tablespoons of butter in the pan drippings. Add sliced mushrooms and diced onions. Cook for 5 to 6 minutes, stirring occasionally, until onions are soft and mushrooms are deeply caramelized. Add minced garlic and cook for 1 minute until fragrant.
Pour in beef broth, Worcestershire sauce, Dijon mustard, and remaining 1 tsp salt and 1/2 tsp black pepper, stirring and scraping up all savory browned bits from the pan bottom.
Bring broth to a rolling boil. Add uncooked wide egg noodles, submerging them into the liquid. Cover with a lid, reduce heat to medium-low, and simmer for 7 to 8 minutes until noodles are tender and sauce has reduced, stirring occasionally.
Remove lid and reduce heat to low. Return the seared beef strips and resting juices to the pan, simmering for 1 minute.
Remove Dutch oven from direct heat. Stir in thick sour cream, folding gently until it melts completely into a rich, silky, velvety stroganoff sauce.
Garnish generously with freshly cracked black pepper and chopped fresh parsley. Serve warm immediately.