Cook the egg noodles: Bring a pot of salted water to a boil and cook the egg noodles according to package directions until tender. Drain and set aside.

Brown the ground beef: Heat a large skillet over medium-high heat and cook the ground beef, breaking it into small crumbles, until no pink remains and the edges turn golden, about 6 to 8 minutes. Drain excess fat and remove the beef to a plate.

Soften onion and mushrooms: In the same skillet, add the onion and mushrooms and cook over medium heat until the onion turns translucent and the mushrooms shrink and release their liquid, about 5 minutes. Stir in the garlic and cook for 30 seconds until fragrant.

Melt butter into the pan: Push the vegetables to one side and add the butter to the empty space, letting it melt and pick up the browned bits from the bottom of the pan.

Make the roux: Sprinkle the flour over the butter and vegetables and stir constantly for about 1 minute, until the mixture turns a pale golden color and smells toasted.

Whisk in the broth: Pour in the beef broth slowly while whisking continuously to prevent lumps. Keep whisking until the sauce is smooth.

Simmer the sauce: Bring the sauce to a gentle simmer and cook for 4 to 5 minutes, stirring often, until it thickens enough to coat the back of a spoon.

Return the beef: Lower the heat and stir the browned ground beef back into the skillet, mixing until evenly coated with the sauce.

Stir in sour cream: Remove the skillet from direct heat and fold in the sour cream, stirring gently until smooth. Season with salt and black pepper to taste.

Combine with noodles: Add the cooked egg noodles to the skillet and toss gently until the noodles are coated with the sauce. Warm through over low heat for 1 to 2 minutes if needed.

Serve: Spoon the stroganoff into bowls and sprinkle with chopped fresh parsley before bringing it to the table.