Bring a large pot of salted water to a boil. Add the egg noodles and cook according to package directions until al dente. Drain well and set aside.

While the noodles are cooking, heat a large skillet or Dutch oven over medium-high heat. Add the ground beef and cook, breaking it up with a spoon, until fully browned. Drain any excess grease from the skillet and set the beef aside.

Add the olive oil to the same skillet (no need to clean it). Reduce heat to medium. Add the chopped onion and cook for 5-7 minutes, until softened and translucent. Add the minced garlic and sliced mushrooms and cook for another 5-7 minutes, until the mushrooms are tender and have released their liquid, which has mostly evaporated.

Sprinkle the all-purpose flour over the onion and mushroom mixture. Cook for 1 minute, stirring constantly, to cook out the raw flour taste.

Gradually whisk in the beef broth, Worcestershire sauce, and Dijon mustard. Bring the mixture to a simmer, stirring occasionally. Let it simmer for 3-5 minutes, or until the sauce has thickened slightly.

Reduce the heat to low. Return the cooked ground beef to the skillet. Stir in the salt and black pepper.

In a small bowl, whisk the room temperature sour cream until smooth. To prevent curdling, temper the sour cream by gradually stirring in a ladleful or two of the hot sauce from the skillet into the sour cream. Then, pour the tempered sour cream mixture back into the skillet with the beef and sauce. Stir gently until fully combined and heated through. Do not boil after adding sour cream, as it can curdle.

Add the drained cooked egg noodles directly into the skillet with the stroganoff sauce. Toss gently to coat all the noodles evenly.

Serve hot, garnished with fresh chopped parsley.