Preheat the oven to 350°F. In a large baking dish, combine the chopped onion, carrots, celery, wild rice, and chicken broth. Cover tightly with foil and bake for 1 hour and 15 minutes.
While the rice is cooking, melt 4 tablespoons of butter in a saucepan over medium heat. Add the flour, salt, and poultry seasoning. Cook for 1 minute before gradually whisking in the milk until you form a smooth, creamy sauce.
Melt the remaining 6 tablespoons of butter and toss it with the cubed bread. If you prefer a casserole without this topping, feel free to skip this step.
Once the rice is cooked, remove it from the oven and take off the foil. Add in raw chicken pieces along with your creamy sauce and stir everything together until well combined. Finally, arrange your buttered bread cubes evenly on top.
Increase your oven temperature to 450°F and bake uncovered for an additional 20-30 minutes. You’ll know it’s done when the chicken is fully cooked (no longer pink) and the bread cubes are golden brown.
After baking, garnish your casserole with salt, pepper, or fresh parsley for an added touch of flavor and color. Dig in and enjoy this comforting dish!