Boil the Noodles: Cook 8 oz of egg noodles in a large pot of salted boiling water according to package directions. Drain and set aside.

Sear the Steak: Heat 2 tbsp olive oil in a large skillet over high heat. Add the 16 oz of sliced sirloin in a single layer, seasoning with salt and pepper. Sear for 1-2 minutes per side until browned. Remove the meat from the pan and set aside.

Saute Mushrooms and Onions: In the same skillet, melt 3 tbsp unsalted butter over medium heat. Add the 1 thinly sliced medium yellow onion and 8 oz sliced baby bella mushrooms. Cook for 5-7 minutes until the vegetables are softened and browned. Stir in 3 cloves minced garlic and cook for 1 minute.

Create the Gravy Base: Sprinkle 2 tbsp all-purpose flour over the mushroom and onion mixture. Stir well and cook for 1 minute to remove the raw flour taste.

Simmer the Sauce: Gradually whisk in 1.5 cups low-sodium beef broth, 1 tbsp Dijon mustard, and 1 tbsp Worcestershire sauce, scraping up any browned bits from the bottom of the pan. Bring to a gentle simmer and let it thicken for 3-5 minutes.

Incorporate Sour Cream and Meat: Reduce the heat to low. Stir in 0.5 cup room-temperature sour cream until completely smooth. Return the seared steak strips and any resting juices to the skillet. Heat through gently for 1-2 minutes, being careful not to boil.

Garnish and Serve: Serve the savory meat and mushroom gravy warm over the prepared egg noodles. Garnish with 2 tbsp chopped fresh parsley.