Preheat the oven, and prep the potatoes. Preheat oven to 500°F with the rack in upper third. Peel the potatoes (if desired), and slice into 1-inch thick rounds.
Season the potatoes. Toss potatoes with butter, thyme, salt, and pepper. Transfer to a 13-by-9 inch metal baking dish and arrange in a single layer. (Don’t use a glass pan, which can crack under such high heat.)
Roast the potatoes, and add the stock. Bake 15 minutes, flip the potatoes, then bake 15 minutes more. Remove the dish from the oven and add chicken stock and garlic cloves. Return to the oven until most of the stock is absorbed, about 15 minutes more.
Serve the potatoes. Transfer to a serving platter and pour any remaining liquid in the pan overtop. Serve warm.
