Pat the 1 ½ lb beef sirloin steak thinly sliced against the grain into strips about 1/4-inch thick strips dry with paper towels and season generously with ½ tsp kosher salt and ½ tsp black pepper freshly ground. Drying the beef is key — it ensures a good sear rather than steaming.

Bring a large pot of salted water to a boil. Cook the 12 oz wide egg noodles according to package directions until just al dente. Drain, toss with a tiny drizzle of vegetable oil to prevent sticking, and set aside.

Heat 1 tablespoon of the vegetable oil in a large skillet over high heat until just smoking. Add the 1 ½ lb beef sirloin steak thinly sliced against the grain into strips about 1/4-inch thick strips in a single layer — work in two batches to avoid crowding. Sear for 1–2 minutes per side until browned but not fully cooked through. Transfer to a plate and set aside. The beef will finish cooking in the sauce.

Reduce heat to medium-high. Add the remaining 1 tablespoon of vegetable oil and the 2 tbsp unsalted butter to the same skillet. Once the butter melts, add the diced yellow onion finely diced and cook, stirring occasionally, for 3–4 minutes until softened and translucent.

Add the sliced cremini mushrooms sliced 1/4-inch thick to the skillet. Cook undisturbed for 2 minutes to allow them to brown, then stir and continue cooking for another 2–3 minutes until the mushrooms are golden and any liquid they release has evaporated. Add the minced cloves garlic minced and cook for 30 seconds until fragrant.

Sprinkle the 2 tbsp all-purpose flour over the mushroom mixture and stir well to coat everything evenly. Cook for 1 minute, stirring constantly, to cook out the raw flour taste.

Pour in the 1 ½ cups beef broth low-sodium preferred while stirring continuously, scraping up any browned bits from the bottom of the skillet. Add the 1 tbsp Worcestershire sauce and 1 tsp Dijon mustard. Bring to a simmer and cook for 3–4 minutes, stirring occasionally, until the sauce thickens enough to lightly coat the back of a spoon.

Reduce the heat to low. Return the seared 1 ½ lb beef sirloin steak thinly sliced against the grain into strips about 1/4-inch thick strips and any accumulated juices on the plate back to the skillet. Simmer gently for 2–3 minutes until the beef is just cooked through and tender.

Remove the skillet from the heat. Stir in the room-temperature 1 cup sour cream full-fat until fully incorporated and the sauce is smooth and creamy. Do not boil after adding the sour cream or it may curdle. Taste and adjust seasoning with ½ tsp kosher salt and ½ tsp black pepper freshly ground.

Serve the stroganoff immediately over the cooked 12 oz wide egg noodles. Garnish with freshly chopped fresh parsley chopped if desired.