Preheat the oven to 400° F / 204°C. Wash and peel the potatoes. Thinly slice the potatoes using a food processor or mandolin. Slice the potatoes into approximately ¼ inch thick slices, not paper thin.
Using the flat side of a knife, carefully smash the garlic clove but leave it whole. In a large, heavy bottomed pot combine the heavy cream, the smashed garlic clove, bay leaves, kosher salt, pepper, nutmeg, and optional sprig of thyme. Bring to a simmer over medium high heat.
When the cream comes to a simmer, turn the heat down and add the potato slices. Gently stir the potatoes to ensure they are all covered by the cream mixture. Simmer for 7 to 10 minutes, gently stirring often until the potatoes are barely fork tender. Do not overcook to potatoes or they may begin to fall apart.
While the potatoes are cooking, prepare the baking dish. Lightly grease a 9x13 inch baking dish or other casserole dish with non-stick spray and set aside.
When the potatoes are just fork tender, remove from the heat. Remove the bay leaves, garlic clove, and thyme sprig if using. Use a slotted spoon to lift out half of the potato slices and place in the greased baking dish. Spread out the potatoes evenly and cover with half of the shredded Gruyère cheese. Top with the remaining potato slices.
Carefully pour over enough of the hot cream to just cover the potatoes. You may not need to use all of the cream; discard the excess. Top with the remaining shredded cheese. Bake for 20 to 25 minutes until the top is well browned, the cream is bubbling, and the potatoes are tender. Let cool slightly before serving and enjoy!
Notes
*Kosher salt is less salty than regular table salt. If using table salt be sure reduce the amount by half. Use 1 tsp of table salt in this recipe instead of 2 tsp kosher salt.