Heat olive oil in a large skillet over medium-high heat. Add the ground beef and cook until browned, breaking it up with a spoon. Drain any excess grease. Add the chopped onion and sliced mushrooms, cooking until softened (about 5-7 minutes). Stir in the minced garlic and cook for one more minute until fragrant.

Sprinkle the flour over the beef mixture and stir until combined. Cook for 1 minute. Gradually pour in the beef broth, stirring constantly. Add the Worcestershire sauce and Dijon mustard, then bring to a simmer.

Reduce the heat to low and simmer for 5-7 minutes, allowing the sauce to thicken. Remove the skillet from the heat and let it cool slightly for a minute.

Stir in the room temperature sour cream until smooth and fully incorporated. Be careful not to let the sauce boil. Season with salt and pepper to taste.

Serve the stroganoff immediately over hot cooked egg noodles and garnish with fresh parsley.