01 - Preheat oven to 350°F. Grease a 9x13-inch casserole dish with cooking spray or butter.
02 - In a large skillet over medium heat, cook ground beef until browned and no longer pink, breaking it up with a wooden spoon. Drain excess fat.
03 - Add chopped onion and minced garlic to the skillet. Sauté for 2–3 minutes until softened and fragrant.
04 - Stir in frozen mixed vegetables. Cook for 2 minutes to thaw slightly.
05 - Remove skillet from heat. Add uncooked rice, 1 cup shredded cheddar cheese, sour cream, milk, cream of mushroom soup, beef broth, salt, black pepper, smoked paprika, dried thyme, and cayenne pepper if using. Mix thoroughly to combine all ingredients.
06 - Spoon the mixture evenly into the prepared 9x13-inch casserole dish, spreading smooth.
07 - Cover the dish tightly with aluminum foil. Bake for 35 minutes.
08 - Remove foil and sprinkle remaining 1 cup shredded cheddar cheese evenly over the top. Bake uncovered for an additional 10 minutes until cheese is bubbly and lightly golden.
09 - Let the casserole rest for 5 minutes before serving to allow the cheese to set and make serving easier.