Cook the gluten-free pasta for 2 minutes less than the package directions. Drain, return to the pot, and toss with the butter. Cover to keep the pasta from drying out.

While the pasta cooks, heat a large Dutch oven over medium heat. Add the ground beef and 1 teaspoon of salt. Cook until browned, breaking the beef apart as it cooks. Drain the excess grease and set the beef aside.

Add the olive oil to the Dutch oven. Add the onion, mushrooms, remaining 1 teaspoon salt, and garlic powder. Cook for 5–10 minutes, or until the vegetables are tender.

Sprinkle in the gluten-free flour, then add the Dijon mustard, ketchup, and Worcestershire sauce. Return the cooked ground beef to the Dutch oven and mix well.

Slowly pour in the beef broth, whisking continuously until incorporated. Bring the mixture to a simmer and cook for about 5 minutes, stirring occasionally.

Add the sour cream and mix until the sauce is smooth and creamy.

Gently fold the cooked pasta into the beef and sauce. Season with additional salt and pepper to taste.

Remove from the heat, cover, and let rest for about 5 minutes. Garnish with fresh parsley and serve warm.