Preheat the oven to 400°F.

In a small saucepan add heavy cream, garlic, nutmeg and 3 tablespoons of the butter and set over low heat.

Using a mandolin, slice the potatoes into ⅛ inch thick and immediately place in a large bowl of cold water. Once all potatoes are sliced, rinse and pat completely dry.

Peel and thinly slice the shallots on the mandolin.

Using 1 tablespoon of butter lightly grease a 12 inch cast iron pan or a 9X13 baking dish.

Arrange a single layer of potatoes on the bottom of the pan, lightly season with salt, thyme then add a thin layer of shallots and sprinkle with gruyere cheese. Continue this process of layering until potatoes, shallots and thyme are all used up. (Be sure to reserve a little cheese for the top.)

Slowly pour the warm cream mixture over the potatoes and gently press down on the potatoes with your hands to make sure all liquid is evenly dispersed. Sprinkle with remaining gruyere, parmesan cheese and remaining 1 tablespoon of thyme.