Classic Beef Stroganoff

Bring a large pot of salted water to a boil and cook the egg noodles according to package directions until tender; drain and set aside.
Pat the beef strips dry and season with 1/2 tsp of the salt and 1/4 tsp of the pepper, then toss with 1 tbsp of the flour.
Melt 1 tbsp of the butter in a large skillet over high heat until it just starts to brown.
Sear the beef in a single layer, undisturbed, for 1 to 2 minutes per side until browned but still pink in the center; work in batches if needed to avoid crowding, then transfer to a plate.
Add the remaining 2 tbsp butter to the skillet and reduce heat to medium; add the onion and cook 4 minutes, stirring, until softened.
Add the mushrooms and cook 6 to 7 minutes, stirring occasionally, until they release their liquid and turn golden brown at the edges.
Stir in the garlic and cook 30 seconds until fragrant.
Sprinkle in the remaining 2 tbsp flour and stir constantly for 1 minute to cook off the raw flour taste.
Slowly whisk in the beef broth, scraping up any browned bits, and bring to a simmer; cook 4 to 5 minutes until the sauce thickens enough to coat the back of a spoon.
Reduce the heat to low and stir in the Dijon mustard and sour cream until smooth; do not let the sauce boil after adding the sour cream or it may curdle.
Return the beef and any accumulated juices to the skillet and warm through for 2 minutes, until the beef reaches your desired doneness.
Season with the remaining 1/2 tsp salt and 1/4 tsp pepper to taste.
Serve the stroganoff spooned over the buttered egg noodles.
Garnish with chopped parsley.