Cook the rice — In a pot, combine rice, 3 cups chicken stock, and ½ teaspoon salt. Bring to a simmer, cover, and cook until tender and the liquid is absorbed. The grains should be soft but not mushy.
Season the chicken — Toss the chicken pieces with remaining salt, garlic powder, and paprika so every piece is coated.
Brown the chicken — Heat olive oil in a large pan over medium heat. Add the chicken and cook until lightly golden and just cooked through. You should hear a steady sizzle, not a loud fry.
Start the sauce — Melt butter in the same pan. Stir in flour and cook for about a minute until it smells slightly nutty and looks smooth.
Add liquid slowly — Pour in milk and remaining stock while whisking. Let it simmer until thick enough to coat a spoon.
Melt the cheese — Stir in the cheddar until fully melted and glossy. The sauce should look creamy but still a little loose.
Combine everything — Add cooked rice, broccoli, and chicken to the sauce. Stir until evenly coated.
Assemble and bake — Transfer to a baking dish, sprinkle parmesan on top, and bake until bubbling and lightly golden on top.
Rest before serving — Let the casserole sit 5–10 minutes so it sets slightly and stays creamy when scooped.