Add the oil to a large skillet over medium heat. Once the oil is hot, add the ground beef.
Brown the beef for about 5 minutes, breaking it up with a wooden spoon until it’s about 80% browned. It’s OK for some of the beef to still be pink.
Add the mushrooms, onions, garlic, salt, and pepper to the beef. Continue to cook, stirring occasionally, for another 5-7 minutes or until the onions are translucent and the mushrooms are cooked down.
Sprinkle the flour over the ground beef and sliced mushrooms. Use a stirring spoon to mix it together.
Add the Worcestershire sauce or coconut aminos, Dijon mustard, and beef broth. Stir until well combined.
Increase the heat to medium-high and bring the mixture to a simmer for 3-4 minutes, or until the sauce thickens slightly.
Remove the skillet from the heat and stir in the sour cream. Let everything sit for 5-10 minutes in the skillet before serving. This time allows the sauce to thicken further.
Gently toss the beef and sauce with the egg noodles or serve the stroganoff over the noodles.
Garnish with minced parsley. Season with additional salt and pepper to taste.