Butter or lightly oil a baking dish or cast iron skillet.
Place the sliced potatoes in a bowl and season generously with salt and pepper. Add the thyme and half of the cheese and toss together.
Transfer to the dish and pour on the milk. It should just cover the potatoes.
Bake 30 minutes, remove from oven and carefully drain off a bit of the liquid (about 1/3 cup as original recipe is written). Sprinkle the remaining cheese over the top and return to the oven.
Bake another 45-50 minutes, until the milk is absorbed, the potatoes are soft and the top and edges are golden. (Optional: drain off a bit more of the liquid as using low-fat milk instead cream can result in a bit of wateriness.)
Let rest at least 20 minutes before serving so the juices can redistribute.
Can be made ahead of time and reheated in the microwave or oven for serving.
*You can substitute other cheeses besides parmesan, such as gouda or asiago. *You can use cream or half and half instead of low-fat milk, but it will add a lot more fat and calories overall. *Nutrition information is a rough estimate.