Finally, I placed the dish into a preheated oven so it could cook for two hours, as recommended.
Since the dish didn't call for the ingredients to be drenched in any liquid, the top layer of potatoes became crunchy well before baking was completed. To allow even cooking without burning the top, I covered it with foil for the rest of the time in the oven.
After checking in on it periodically, my casserole actually took about 65 minutes to cook — I'm glad I didn't leave it in for the full two hours.