Preheat the KitchenAid® Double Wall Oven to 400° F. Using a mixing bowl, mix together the grated cheeses, heavy cream, garlic and thyme. Season with salt and pepper and add in the potato slices, a handful at a time, and toss together so that the potatoes become lightly coated with the cream mixture.

As you finish coating each handful of potatoes, place into a separate dish until all of the potatoes and yams have gone through the heavy cream mixture.

Grease a KitchenAid® 3.5-Quart Casserole Dish with butter. Pick up a handful of potatoes at a time, organizing them into a nice, even stack and lay them in the Casserole Dish with their edges aligned vertically. Continue placing potatoes in the dish, working around the perimeter and into the center until all the potatoes have been added.

I also place yam slices in between the potatoes. Place yam slices in between the potato stacks in whatever pattern you choose.

The potatoes should be very tightly packed. If you need to, slice an additional potato, coat lightly with the cream mixture and add to the casserole. Sprinkle on some extra freshly grated parmesan cheese if desired.

Cover the dish tightly with aluminum foil and transfer to the oven. Bake for 30 minutes. Remove the foil and continue baking for another 45 minutes or until golden brown and crisp on top. Carefully remove from the oven and let rest for a few minutes. Serve immediately.