Preheat your oven to 350°F (175°C).

In a large pot over medium-high heat, brown the ground beef. Season with salt, pepper, and Italian seasoning while cooking. Drain excess grease and transfer the beef to a plate. Cover with foil to keep warm.

In the same pot, melt 2 tablespoons of butter. Add diced onions and sauté for about 5 minutes until softened. Then add minced garlic and cook for an additional minute.

Pour in the beef broth along with the remaining tablespoon of butter and the uncooked rice. Stir to combine. Bring to a boil, then reduce heat to a simmer.

Cover the pot tightly and allow the rice to cook for 10 minutes. Then add the sliced mushrooms, replace the cover, and continue cooking for another 5 to 10 minutes.

Turn off the heat and leave the pot covered for 10 minutes.

Add the cooked ground beef back into the pot along with the cream of mushroom soup, milk, sour cream, and half of the cheddar cheese. Stir until evenly combined.

Lightly grease a 9x13 inch casserole dish. Transfer the mixture into the dish and spread evenly. Sprinkle the remaining cheese on top.

Cover the casserole dish with foil and bake for 20 minutes until the cheese is melted and bubbly.