Season the beef strips with salt and black pepper. Heat olive oil and butter in a large skillet over medium-high heat. Sear the beef strips for 1–2 minutes per side until browned, cooking in batches if necessary. Transfer the beef to a plate and set aside.
In the same skillet, melt 1 tablespoon of butter over medium heat. Add onions and garlic, sautéing until softened (about 3 minutes). Stir in the sliced mushrooms and cook until golden brown (about 5 minutes).
Sprinkle in smoked paprika and Dijon mustard, stirring well. Pour in white wine (or beef broth), scraping up any browned bits from the bottom of the pan for extra flavor. Let it simmer for 2 minutes, allowing the alcohol to cook off.
Add beef broth and Worcestershire sauce, stirring to combine. Lower the heat and stir in the sour cream, making sure it blends smoothly into the sauce. Add fresh thyme and season with salt and pepper to taste.
Add the seared beef strips back into the skillet, tossing them in the sauce for 1–2 minutes until warmed through. Serve immediately over cooked egg noodles, garnished with chopped parsley.
Notes
For an extra creamy dish, ensure the sour cream is well incorporated into the sauce. Serve over egg noodles for a classic presentation.