Preheat your oven to 190°C (170°C fan/Gas Mark 5). Lightly grease a 9x13 inch baking dish.

Heat the olive oil in a large, oven-safe pan or Dutch oven over medium-high heat. Add the cubed chicken and cook for 5-7 minutes, stirring occasionally, until it's lightly golden on all sides and no longer pink. You’ll hear a gentle sizzling sound and see the chicken turning opaque. Remove the chicken from the pan and set aside.

In the same pan, add the chopped onion and cook for 3-4 minutes until it softens and becomes translucent, releasing a sweet aroma. Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it.

Sprinkle the plain flour over the onion and garlic mixture, stirring constantly for 1 minute. It will form a thick paste. This step helps create the roux for our creamy sauce.

Gradually pour in the chicken stock and milk, whisking continuously to prevent lumps. The mixture will begin to thicken and bubble gently; you'll see it transform into a smooth, velvety sauce. Stir in the dried mixed herbs, salt, pepper, and optional smoked paprika.

Add the uncooked rice and broccoli florets to the sauce, stirring well to combine. Return the cooked chicken to the pan. Bring the mixture to a gentle simmer, then pour the entire contents into your prepared baking dish.

In a separate bowl, combine the grated cheddar, mozzarella, and cream cheese. Scatter about two-thirds of this cheesy mixture evenly over the top of the casserole.

Cover the baking dish tightly with aluminium foil and bake for 25 minutes. After this time, carefully remove the foil. The rice should be partially cooked, and the casserole will be bubbling with steam.

Sprinkle the remaining cheese over the top and return the dish to the oven, uncovered, for another 10-15 minutes, or until the cheese is melted, golden brown, and delightfully bubbly, and the rice is tender. The top will be gloriously browned, and the edges will be making little happy sizzling noises.

Once baked, remove the casserole from the oven and let it rest for 5-10 minutes before serving. This allows the sauce to set slightly and makes for easier, neater serving.