Cooked turkey may be used instead of chicken. Use any type of cooked rice. If desired, substitute two 10¾-ounce cans condensed cream of mushroom or chicken soup mixed with ½ cup milk and ½ cup chicken broth for the butter/mushroom/flour/chicken broth/milk mixture.
Preheat the oven to 400°F. Grease a 13 × 9-inch baking dish.
Melt in a large saucepan over medium heat:
Stir in and cook until softened, about 5 minutes:
Stir in until well blended:
Slowly add while whisking:
Bring to a boil, reduce the heat, and cook until the sauce is thickened and smooth, about 5 minutes. Mix in:
Pour into the prepared dish. Mix together and sprinkle on top:
Bake until the sauce is bubbling and the topping is golden brown, 25 to 35 minutes.