Preheat the oven to 350℉ (180℃).
Rinse the wild rice with cold water; drain.
Heat the chicken broth to boiling and add the wild rice. Boil for 15 minutes, then remove from the heat. (Why this extra step with the wild rice? Because it takes longer to cook than long-grain white rice). Drain the wild rice in a sieve or fine strainer over a large liquid measuring cup, retaining the liquid. Top off the liquid in the measuring cup with more chicken broth if needed, to 3½ cups.
While the wild rice is cooking on the stove top, prepare the spice rub and rub it into the chicken on all sides. Set aside.
In a 2-quart casserole (or 9x13 baking pan), add the chopped celery and onion evenly over the bottom, then evenly distribute the 5 tablespoons of butter in the pan. Bake in the oven for 12-14 minutes; remove from the oven.
Into the casserole or baking pan, add the broth (topped off to 3½ cups if needed), and the white and wild rice into the aromatics and stir. Top it with the seasoned chicken, cover it with foil and bake for 30 minutes.
After 30 minutes, remove the pan from the oven and remove and discard the foil. Spray each exposed chicken piece with cooking spray, or brush on a light coating of cooking oil. This step will ensure the chicken browns and creates a crispy top.
Return the pan to the oven, this time uncovered. Bake for another 20 minutes or so, until the rice liquid is absorbed. Test the chicken for doneness, it should reach a minimum of 165℉. Keep an eye on both the rice (so it doesn't dry out) and the chicken (so that it reached the safe eating temperature). Your cooking time will vary depending on whether you use a glass or metal pan - glass does not conduct the heat as well as metal and will likely take longer.
Remove from the oven and briefly remove the chicken so you can give the rice a good stir. Return the chicken to the pan, and let the dish stand for about 5 minutes before serving.