Peel the potatoes and slice them to 1/8 inch thin slices. I reccomend using a mandoline or a food processor.

Spray a 3 quart baking dish with cooking spray. Layer half of the potatoes evenly over the bottom of the dish. Sprinkle with salt and pepper.  

In a bowl, mix the cheeses with the cornstarch. Sprinkle half of the cheese mixture over the potatoes in the baking dish.

Layer the rest of the potatoes over the cheese and sprinkle with salt and pepper.

In a bowl, combine the half and half and the chicken broth. Pour it over the potatoes. Then sprinkle the rest of the cheese over the top.

Cover and bake for 45 minutes. Uncover and bake for the remaining 20 minutes, or until the potatoes are cooked through and are fork tender.