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- Softened butter
- 1 clove garlic, smashed
- 1kg potatoes, peeled
- kosher salt
- pepper
- 8 to 10 fresh thyme sprigs
- freshly grated nutmeg, optional
- 1.5 cups (or more or less) stock
- 1.5 cups (or more or less) heavy cream
- 1 heaping cup grated Gruyère cheese
- 1/4 cup grated Parmigiano Reggiano cheese
- Preheat oven to 190c (375ºF). Grease an earthenware gratin dish with smashed peeled garlic and butter.
- cut potatoes 1/8-inch thick and layer overlapping slices in the prepared pan. Season generously with salt, pepper, and thyme leaves (no need to chop — just pull and scatter). Lightly grate nutmeg over top. Make another layer of potato slices and season again in the same manner.
- Cover the potatoes with the stock and cream — you may need more to allow the liquid to get to the top level of the top layer of potatoes.
- Sprinkle the top with the grated cheeses.
- Bake 45 minutes to 1 hour (see notes above if you need to make this ahead of time), checking after 40 minutes or so to make sure the potatoes are not browning too quickly. If they are browning too quickly, cover the pan with foil and continue baking until the potatoes are tender and the top is nicely browned. You can also turn the temperature down to 350ºF if necessary. I find this consistently takes over an hour for the liquid to thicken up and for the top to be evenly browned.