Preheat your oven to 350°F. In a large baking dish, combine the chopped onion, carrots, celery, wild rice, and chicken broth. Cover the dish tightly with foil and bake for 1 hour and 15 minutes. While the rice cooks, melt 4 tablespoons of butter in a saucepan over medium heat. Stir in the flour, salt, and poultry seasoning, cooking for about 1 minute. Gradually whisk in the milk, stirring constantly until you have a smooth, creamy sauce. For the optional topping, melt the remaining 6 tablespoons of butter and toss it with the cubed bread. (If you prefer to skip the topping, you can leave this step out.) When the rice is done, remove the foil and add the raw chicken pieces and creamy sauce to the baking dish. Mix everything well to combine, then evenly spread the buttered bread cubes on top. Increase the oven temperature to 450°F and bake uncovered for 20 to 30 minutes, or until the chicken is cooked through and no longer pink, and the bread cubes are golden brown. Once baked, season with salt, pepper, or fresh parsley for a burst of flavor and color. Serve and enjoy!