01 - Preheat oven to 350°F. Grease a 9x13-inch casserole dish with cooking spray or butter.
02 - Heat a large skillet over medium heat. Add ground beef and cook until browned, breaking up with a spoon, about 6-8 minutes. Drain excess fat.
03 - Add chopped onion and minced garlic to the skillet. Sauté for 2-3 minutes until onion is softened and fragrant.
04 - Stir in frozen mixed vegetables and cook for 2 minutes until heated through.
05 - Remove skillet from heat. Add uncooked rice, 1 cup cheddar cheese, sour cream, milk, cream of mushroom soup, beef broth, salt, pepper, smoked paprika, dried thyme, and cayenne pepper. Mix thoroughly until well combined.
06 - Spoon the mixture evenly into the prepared 9x13-inch casserole dish, spreading into an even layer.
07 - Cover dish tightly with aluminum foil. Bake for 35 minutes until rice is tender and mixture is bubbling.
08 - Remove foil and sprinkle remaining 1 cup cheddar cheese evenly over the top. Return to oven uncovered and bake for 10 minutes until cheese is melted and bubbly.
09 - Let casserole rest for 5 minutes before serving to allow flavors to meld and make serving easier.