Cook the egg noodles according to the package instructions. Drain and set them aside.While that’s happening, slice your sirloin into two lengthwise pieces, then cut into thin 1/8-inch strips. In a medium bowl, toss the beef strips with Worcestershire sauce and dried thyme. This helps tenderize the meat and infuse it with flavor.
Heat vegetable oil in a large skillet over medium-high heat. Add the beef in a single layer and sear for 1 to 2 minutes, just until mostly browned (don’t overcook—it’ll finish cooking later). Remove the meat from the pan and set it aside.
In the same pan, melt butter over medium heat. Add the mushrooms, diced onion, and garlic. Sauté for 5 to 7 minutes, or until the onions turn translucent and the mushrooms are golden and fragrant.
Sprinkle in the paprika, kosher salt, black pepper, and flour. Stir well to coat the mushrooms and absorb the butter.
Slowly pour in the white wine, just a tablespoon at a time. Stir constantly to deglaze the pan, scraping up those flavorful browned bits. Once the wine is mostly absorbed, whisk in the beef broth.
Bring the mixture to a boil, then reduce the heat to a simmer. Let it reduce slightly—about 2 minutes—until the sauce thickens. Remove the skillet from the heat and stir in the sour cream until smooth and creamy.
Return the browned beef and any juices to the pan. Stir gently to coat the meat in the sauce. Taste and adjust with more salt or pepper if needed (I usually add another 1/2 teaspoon of kosher salt and a pinch of pepper at this point).
Serve the beef stroganoff over the warm egg noodles, and top with freshly chopped parsley for a burst of color and freshness.