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1
Preheat the oven to 450u00b0F.
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2
Wash the potatoes, place in a sauce pot, and cover them with cold water and a teaspoon of salt. Bring the potatoes to a boil and simmer for 20 minutes, or until they're cooked through. Drain and keep them warm.
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3
To make the white sauce, melt the butter in a saucepan on medium heat, add the flour to form a roux, and cook it for 30 seconds while stirring constantly. Take the pan off the heat, and allow the roux to cool slightly. Add the milk and whisk until the roux is thoroughly dispersed into the milk. Return the pan to the stove and cook the mixture over medium heat. Stir the sauce continuously until it thickens, 5 to 10 minutes.
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4
Insert the clove and bay leaf into the onion (this is called onion pique), and add to the sauce. Cover the saucepan tightly with a lid or foil, and place it into a larger pan of simmering water for 30 minutes; the water should come to or above the level of the sauce in the smaller saucepan. When the sauce is cooked, remove and discard the onion pique. Season the sauce with salt, pepper, and nutmeg, and add the heavy cream. Keep the sauce warm in the water bath until needed.
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5
Grill the bacon slices until they're crisp; cut them at right angles into 1/4-inch strips. Cut the cooked potatoes into 1/4-inch-thick slices.
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6
In a bowl, mix the potatoes, four-fifths of the bacon, and enough sauce to lightly bind the two. Add half of the cheese and mix together thoroughly. Pour this mixture into a buttered 2-quart gratin dish. Top the mixture with the remaining sauce, cheese, and bacon and bake until it's golden brown, 15 to 20 minutes. Sprinkle the tartiflette with chives and serve.
