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1
Preheat the oven to 375F.
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2
Butter a 14-inch oval gratin dish with 1 tablespoon of the butter.
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3
Put the cream, stock, bay leaf, and salt in a medium pot, and stir to combine.
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4
Bring the mixture to a simmer, reduce the heat to low, and let steep while you prepare the potatoes.
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5
Peel the potatoes.
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6
Use a mandoline slicer or a knife to cut the potatoes into 1/8-inch-thick slices.
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7
Neatly layer the slices in the gratin dish, overlapping slightly, like shingles on a rooftop, making 3 or 4 layers.
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8
Its important to slice the potatoes and immediately assemble the gratin, before the potatoes oxidize and turn brown.
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9
Avoid putting the potatoes in water.
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10
You dont want to rinse off any of the potato starchthe starch is essential for a rich, creamy gratin.
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11
Remove the bay leaf from the cream mixture and discard.
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12
Gently pour the mixture over the potatoes.
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13
The liquid level should be just below the surface of the potatoes; when you gently press the potatoes down with a spatula, the cream mixture should spill over the top layer of potatoes.
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14
Dot the remaining 2 tablespoons butter on top, and cover tightly with foil.
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15
Bake until the potatoes are almost tender when pierced with a small, sharp knife, about 35 minutes.
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16
Increase the oven temperature to 400F.
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17
Press the potatoes down with a spatula to an even thickness, allowing the creamy juices to baste the top.
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18
Sprinkle the thyme and black pepper on top.
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19
Continue to bake, uncovered, pressing the potatoes down with a spatula to baste periodically, until the gratin is nicely browned, about 30 minutes.
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20
(Its okay if the gratin is a little loose and creamy at this point.)
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21
Remove from the oven and let stand for 5 minutes before serving, to allow the gratin to settle and absorb some of the cream.
