Creating this ultimate comfort dish is straightforward. Follow these steps carefully for a perfectly creamy, cheesy, and satisfying Cheesy Broccoli Rice Casserole every single time.

1. Preheat and Prepare: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish with butter or non-stick cooking spray. Set aside.
2. Prepare the Broccoli: Briefly steam or blanch the fresh broccoli florets until they are bright green and just barely tender (about 3-4 minutes in boiling water, followed by an ice bath, or 3-5 minutes steaming). Drain them thoroughly – excess water can make the casserole runny. Set aside. Ensuring the broccoli is well-drained is a crucial step for achieving the right consistency.
3. Make the Roux: In a large saucepan or Dutch oven, melt the 1/2 cup of unsalted butter over medium heat. Once melted and bubbly, whisk in the 1/2 cup of all-purpose flour. Cook, whisking constantly, for about 1-2 minutes until the mixture is smooth and lightly golden. This step cooks out the raw flour taste and forms the base for thickening the sauce.
4. Create the Béchamel: Gradually whisk the 3 cups of whole milk into the roux. Pour slowly, whisking continuously to prevent lumps from forming. Continue cooking over medium heat, whisking frequently, until the sauce begins to thicken and bubble gently around the edges. This usually takes about 5-7 minutes. The sauce should be thick enough to coat the back of a spoon.
5. Add Cheese and Seasonings: Remove the saucepan from the heat. Stir in the salt, black pepper, garlic powder, and onion powder. Gradually add 3 cups of the shredded sharp cheddar cheese, stirring until the cheese is completely melted and the sauce is smooth and velvety. Stirring off the heat prevents the cheese from becoming grainy or separating.
6. Combine Ingredients: To the saucepan with the cheese sauce, add the 4 cups of cooked white rice and the 4 cups of prepared broccoli florets. Gently fold everything together until the rice and broccoli are evenly coated with the glorious cheese sauce. Ensure you mix gently to avoid breaking up the broccoli florets too much.
7. Assemble the Casserole: Pour the cheesy broccoli rice mixture into the prepared 9×13 inch baking dish. Spread it out evenly with a spatula or the back of a spoon.
8. Add Topping: Sprinkle the remaining 1 cup of shredded sharp cheddar cheese evenly over the top of the casserole. If using the optional cracker or breadcrumb topping, mix the crushed crackers/breadcrumbs with the 1 tablespoon of melted butter, then sprinkle this mixture evenly over the cheese layer. This topping adds a lovely textural crunch.
9. Bake: Place the baking dish in the preheated oven. Bake for 25-30 minutes, or until the casserole is hot, bubbly around the edges, and the cheese topping is melted and lightly golden brown. If the topping starts to brown too quickly, you can loosely tent the dish with aluminum foil.
10. Rest: Once baked, carefully remove the casserole from the oven. Let it rest for at least 10-15 minutes before serving. This crucial resting period allows the cheese sauce to set slightly, preventing it from being too runny and making it easier to serve. The flavors also meld together beautifully during this time.
11. Serve: Scoop generous portions onto plates and serve warm. Enjoy the ultimate cheesy comfort!