First, begin by preheating your oven to 400F and spray a 16 cup muffin tin with nonstick cooking spray. Set aside.Next, finely grate your cheese. Start off by doing half and if you need more, come back to it! Set aside.Slice your sweet potatoes as thin as you can.To make stacks, place on sweet potato sliver onto the bottom of your muffin tin and layer with cheese. Repeat 3-5 times per stack. *Do not sprinkle cheese on top, we will do this later.Lightly spray each stack with more nonstick cooking spray and season with salt and pepper.Place in oven at 400 for 20 minutes. Remove cheese from oven and sprinkle cheese on top. Place back in oven for about 5 minutes or just enough to melt the cheese on top.Before serving clean up the bottom of your stacks. Some of the cheese may have burned a little or become a darker cover, so just use a knife to cut all of the excess cheese off.If you are using bigger sweet potatoes, you may want to cook them a little longer to ensure they are cooked all the way through!