If you do not want to use aluminum foil, then place potatoes on the cooking rack in the middle of the oven, and bake for about 45 minutes at 375F or until tender.
I used heavy duty alum foil. It is not necessary to use it, but the potatoes are cooked much faster and we like it. It is the best if you use the same size potatoes. The cooking time will also vary on the size of your potato. You can use as many as you want as long as it could fit in your oven, but I got to mention that any leftover potatoes makes a fantastic salad the next day.