Preheat your oven to 350 degrees
Place 500ml of whole milk and 500ml of heavy cream into a large pot and bring to a simmer
Add garlic, nutmeg, salt and pepper and mix to combine
Add thinly sliced potatoes and simmer for 5 minutes
Butter a 10x10" baking dish
Using a slotted spoon, transfer half of the potatoes into the base of the dish, leaving the cream behind
Add 1 cup of gruyère over the first half of the potatoes
Add the remaining potatoes
Spoon in enough cream to come to about 1/2 inch from the top of the baking dish (see photo above)
Top with the remaining gruyère
Bake at 350 degrees on a middle rack for 40-45 minutes
Allow the dish to cool for 15 minutes on a cooling rack before slicing
Sprinkle with fresh thyme leaves before serving