Boil the noodles: Bring a large pot of salted water to a boil. Cook egg noodles according to package directions until al dente. Drain and set aside with a drizzle of olive oil to prevent sticking.

Brown the beef: Heat a large skillet over medium-high. Add the ground beef and season with salt and pepper. Cook, breaking it up, until well browned with some crispy bits, about 6–8 minutes. Transfer to a plate and drain excess fat if needed, leaving about 1 tablespoon in the pan.

Sauté the aromatics: Add butter to the skillet. Stir in the onion and cook until softened and lightly golden, 3–4 minutes. Add mushrooms and cook until they release their moisture and brown, about 5–6 minutes. Stir in garlic for 30 seconds until fragrant.

Build the roux: Sprinkle flour over the mushroom mixture and stir well for 1 minute to cook off the raw taste. If using cornstarch instead, skip this step and whisk it later into cool broth.

Deglaze and simmer: Slowly pour in the beef broth while stirring, scraping up browned bits. Add Worcestershire, Dijon, and smoked paprika. Return the beef and any juices to the pan. Simmer gently for 3–4 minutes until the sauce thickens slightly.

Add sour cream: Reduce heat to low. Stir in sour cream until the sauce turns creamy and smooth. Do not boil after adding sour cream to avoid curdling. Taste and adjust salt and pepper.

Combine with noodles: Fold in the cooked noodles or serve the stroganoff over them. Garnish with chopped parsley for freshness.

Serve: Spoon into bowls and enjoy hot. Add an extra dollop of sour cream or a squeeze of lemon for brightness if you like.