In a large pot of boiling salted water, blanch the broccoli florets for about 2-3 minutes until they turn bright green but are still crisp. Drain and immediately plunge them into an ice bath to stop the cooking process. Drain again and set aside.
In a large mixing bowl, combine the cooked rice, 1.5 cups shredded cheddar cheese, cream of mushroom soup, milk, sour cream, garlic powder, onion powder, black pepper, and salt. Stir until well combined.
Gently fold the blanched broccoli into the rice and cheese mixture until evenly distributed.
Pour the broccoli mixture into a greased 9x13 inch casserole dish, spreading it evenly.
In a separate bowl, combine the breadcrumbs with melted butter until well coated. If you like a bit of heat, you can also mix in the red pepper flakes at this stage.
Sprinkle the breadcrumb mixture evenly over the broccoli and cheese layer in the casserole dish. Top with the remaining 0.5 cup of shredded cheddar cheese for an extra cheesy finish.
Place the casserole in the preheated oven and bake for 25-30 minutes, or until the top is golden brown and the cheese is bubbly.
Once baked, remove the casserole from the oven and allow it to cool for a few minutes. Slice and serve warm as a comforting side dish or a main course.
Notes
Adjust salt to taste and add red pepper flakes for heat if desired.