Preheat the oven to 400°

Combine the cooked rice, broccoli, and chicken in the casserole dish and set aside.

Melt the butter in a medium sauté pan over medium heat. Add the onions and cook, stirring, until softened, about 2 minutes. Add the garlic and flour and cook for 1 or 2 minutes, or until the flour begins to brown but doesn’t burn, whisking almost continuously.

Whisk in the milk, watching for lumps, reduce heat and cook until it thickens. Stir in the sour cream, grated cheese, curry powder, salt, and pepper and stir until well combined. Bring to a simmer and cook, stirring, until the mixture is the consistency of gravy, about 3 to 4 minutes.

Pour the sauce in the baking dish and mix thoroughly with the rice, broccoli, and chicken and spread it out evenly in the baking dish.

Bake for 10 to 12 minutes, and then turn it up to a high broil to brown the top for another couple minutes. Serve warm.