Preheat oven to 400°F and spray 12 muffin tin with nonstick spray.
Mix gruyere, parmesan, and ranch dip.
In second bowl, coat sliced potatoes with melted butter and salt.
Layer 4 potato slices and then 1/2 teaspoon of cheese mixture into each tin. Continue until potatoes are taller than tin (4-5 layers total), ending with cheese on top. Stacks will shrink as they cook.
Cover with foil sprayed with nonstick spray. Bake 15 minutes. Remove foil, and continue baking 25-30 minutes until golden brown and bubbly.
Cool 10 minutes before removing stacks from tins. Garnish and serve.