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1
Preheat the oven to 350 degrees F. Rub the bottom of a 9-by-13-inch baking dish with softened butter.
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2
Using a mandoline or a very sharp knife, slice the potatoes very thinly.
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3
They'll cook better that way.
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4
Place the potatoes in the baking dish and sprinkle with 1/2 teaspoon salt and some pepper.
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5
In a large skillet over medium-low heat, melt the butter.
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6
Add the garlic and onions and cook until translucent, stirring occasionally, about 4 minutes.
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7
Cut the bar of cream cheese in half and add the halves to the skillet, stirring constantly.
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8
Continue stirring until the mixture is smooth and combined, about 3 minutes.
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9
Pour in the half-and-half and stir to combine.
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10
Mix in 1/2 teaspoon salt and some pepper.
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11
Taste and adjust the seasonings as necessary.
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12
Do not undersalt!
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13
Add the rosemary and green onions and stir to combine.
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14
Finally, mix in 1/2 cup of the grated Parmesan.
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15
Pour the cream cheese mixture over the top of the potatoes.
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16
Scrape out the skillet to get every last drop.
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17
Sprinkle the remaining 1/2 cup grated Parmesan generously over the top and bake until golden brown and bubbly, at least 1 hour.
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18
Let stand for 10 minutes before serving.
