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1
Preheat the oven to 350F.
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2
Line a plate with paper towels.
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3
Line a baking sheet with a silicone baking sheet, parchment paper, or aluminum foil to protect the baking sheet from spills and make for easy cleanup.
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4
Heat a skillet over medium heat and cook the bacon until brown and crispy, 5 to 7 minutes.
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5
Remove the bacon to the prepared plate, reserving the rendered fat.
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6
Brush an ovenproof gratin dish with some of the rendered bacon fat.
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7
Save the remaining fat for another use or discard.
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8
Peel the potatoes and, preferably using a mandoline, slice them 1/8 inch thick.
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9
Or, using a chefs knife, carefully slice the potatoes thinly and evenly.
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10
Arrange the potatoes in the dish in overlapping layers, seasoning with the reserved bacon, thyme, garlic, and salt and pepper as you go.
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11
Place the gratin on the prepared baking sheet.
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12
Combine the milk, heavy cream, and nutmeg in a medium heavy-bottomed pot.
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13
Bring to a gentle simmer over medium heat.
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14
Pour over the gratin.
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15
Sprinkle the cheese over the top.
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16
Bake until the potatoes are tender and deep golden brown, and the edges are bubbling, about 1 hour.
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17
(If the gratin starts to brown too deeply, cover with aluminum foil.)
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18
Let cool slightly, about 10 minutes, before serving.
