Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.

Follow the package instructions to cook your rice, then set it aside to cool slightly.

Steam the broccoli florets for approximately 4-5 minutes until tender, then drain excess water.

Heat unsalted butter in a skillet over medium heat and sauté chopped onion until soft (about 3-4 minutes).

In a mixing bowl, combine cream of mushroom soup, sour cream, milk, garlic powder, onion powder, salt, and pepper, and stir until smooth.

Fold in 1½ cups of shredded cheddar cheese into the mixture.

Add cooked rice, steamed broccoli, and sautéed onion to the cheese mixture, stirring until well combined.

Spread the mixture into the prepared baking dish and sprinkle remaining cheddar cheese on top.

Cover with foil and bake for 25 minutes, then remove foil and bake for an additional 10-15 minutes until golden brown.

Let the casserole rest for 5-10 minutes before serving to help it set.