Creating Cheesy Mini Gratin Dauphinois Potato Stacks is simple when you follow these steps:

1. Preheat Your Oven: Preheat the oven to 375°F (190°C). Grease a muffin tin with olive oil to prevent sticking.
2. Prepare the Potatoes: Peel the russet potatoes and slice them thinly (about 1/8 inch thick) using a mandoline or a sharp knife.
3. Make the Cream Mixture: In a mixing bowl, combine the heavy cream, whole milk, minced garlic, salt, pepper, thyme, and nutmeg (if using). Whisk until well blended.
4. Layer the Stacks: Place a layer of potato slices in each muffin tin cup. Pour a small amount of the cream mixture over the potatoes, followed by a sprinkle of Gruyère and cheddar cheese.
5. Repeat Layers: Continue layering potatoes, cream, and cheese until the cups are filled, finishing with a layer of cheese on top.
6. Bake: Place the muffin tin in the preheated oven and bake for 35-40 minutes, or until the tops are golden brown and the potatoes are tender when pierced with a fork.
7. Cool: Remove from the oven and let the stacks cool for about 5 minutes before gently removing them from the muffin tin.
8. Serve: Carefully lift the stacks out with a fork and serve warm.

These steps will guide you to create the most delightful Cheesy Mini Gratin Dauphinois Potato Stacks that everyone will love.