Preheat oven to 350°F. Lightly grease a 9x13 casserole dish.

Cook the beef mixture: In a large skillet over medium heat, cook ground beef, onion, and garlic until beef is browned. Season to taste with salt and pepper. Drain excess grease if necessary.

Add mushrooms & seasoning: Stir in mushrooms, salt, pepper, mustard powder and paprika. Cook 4–5 minutes until mushrooms are softened.

Mix the casserole base: In a large bowl, combine uncooked rice, beef broth, cream of mushroom soup, sour cream, beef mixture, mushrooms and 1 cup of the cheese. Stir until evenly mixed.

Assemble: Spread mixture into prepared casserole dish. Cover tightly with foil.

Bake: Bake covered for 60 minutes. Remove foil, fluff up the rice with a fork, sprinkle with extra cheese, and bake 5- 10 minutes more until rice is tender and cheese is bubbly.

Serve: Let rest 5–10 minutes before serving. Garnish with extra sour cream and parsley, if desired