1-First Step: Preparation and Mise en Place Start by preheating your oven to 350°F. This ensures the oven is ready to go as soon as your casserole is assembled. Next, boil a large pot of water. You will need this for blanching the broccoli. While the water heats up, dice your small onion and measure out your spices and other ingredients. Having everything ready (mise en place) makes the cooking process smooth and stress-free. It is also a good time to grease your 2-quart casserole dish so it is ready for the mixture later.

2-Second Step: Building the Flavor Base In a medium saucepan, combine the diced onion and 3 tablespoons of butter. Cook them over medium-low heat, stirring occasionally. You want the onion to soften and become translucent, which usually takes about 3 to 5 minutes. This step sweats the onions, releasing their natural sugars and building a flavorful foundation for the sauce. Be careful not to brown the butter or onions; you want them soft and golden.

3-Third Step: Creating the Roux Once the onions are soft, it is time to thicken the sauce. Stir in the flour, garlic powder, and black pepper. Cook this mixture for about 2 more minutes, stirring constantly. This cooks out the raw flour taste and creates a roux. The mixture should bubble slightly and look pasty. This is crucial for achieving the right consistency for your creamy broccoli rice casserole. Cooking the flour with the fat from the butter is the secret to avoiding a grainy sauce.

4-Fourth Step: Making the Creamy Sauce Gradually whisk in the 2 cups of milk. Do this slowly to prevent lumps from forming. Continue whisking until the mixture is smooth. Bring the heat up slightly and cook until the sauce thickens and becomes bubbly. You will know it is ready when it coats the back of a spoon. This might take a few minutes of gentle boiling. Once thickened, remove the saucepan from the heat immediately to stop the cooking process.

5-Fifth Step: Adding the Cheese Now comes the best part. Stir in the dry mustard powder, paprika, 3 tablespoons of cream cheese, and 1 1/2 cups of the shredded sharp cheddar cheese. Stir until the cream cheese and cheddar are completely melted and the sauce is smooth and uniform. This creates a rich, velvety cheese sauce. Give it a taste and adjust the salt and pepper to your preference. Remember, the cheese adds saltiness, so taste before adding more.

6-Sixth Step: Preparing the Broccoli While your sauce is thickening, your pot of water should be boiling. Add the broccoli florets to the boiling water. Blanch them for just 1 to 2 minutes. You want the broccoli to become bright green but still remain crisp. Do not overcook it here, as it will finish cooking in the oven. Once blanched, drain the broccoli well. Removing excess water is important so your casserole does not become watery.

7-Final Step: Assemble and Bake In a large bowl, combine the cooked white rice, the blanched and drained broccoli, and the delicious cheese sauce you just made. Mix everything until the rice and broccoli are evenly coated in the sauce. Pour this mixture into your greased 2-quart casserole dish. Spread it out into an even layer. Top with the remaining 1/2 cup of shredded sharp cheddar cheese for that golden, bubbly crust. Place the dish in the preheated oven and bake for 35 minutes, or until the cheese is bubbly and lightly browned on top. Let it rest for a few minutes before serving to allow the sauce to set slightly.