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1
Preheat the oven to 400.
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2
Lightly butter a 9-by-13-inch baking dish.
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3
On a baking sheet, toss the sweet potatoes with 1/4 cup of the olive oil, the thyme and 1 teaspoon of salt; season with pepper.
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4
Roast the potatoes for 20 minutes, stirring occasionally, until tender.
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5
Meanwhile, cook the pasta in a pot of salted boiling water until almost al dente, 5 minutes for torchio and 10 minutes for rigatoni.
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6
Drain, rinse under cold water and return to the pot.
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7
In a small saucepan, bring the milk just to a simmer.
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8
In a medium saucepan, melt the 2 tablespoons of butter.
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9
Add the flour and cook over moderately low heat, whisking frequently, until lightly golden, about 3 minutes.
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10
Whisk in the hot milk in 3 additions until incorporated.
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11
Cook over moderate heat, whisking often, until thickened, 10 to 15 minutes.
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12
Stir in the Fontina, the shredded Cantal, 1/4 cup of the Parmigiano and the nutmeg until the cheeses are melted.
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13
Stir in the heavy cream and season with salt and pepper.
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14
Stir the cheese sauce into the pasta.
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15
In a medium bowl, toss the radicchio with the rosemary, the remaining olive oil and 1/2 teaspoon of salt.
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16
Season with pepper and toss, then add to the pasta and mix well.
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17
Spread half of the pasta in the prepared baking dish.
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18
Tuck in half each of the sweet potatoes, cubed Cantal and pecans.
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19
Repeat with the remaining pasta, sweet potatoes, Cantal and pecans.
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20
Sprinkle the remaining 1/2 cup of Parmigiano on top.
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21
Cover the baking dish with foil and bake for 10 minutes.
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22
Uncover and bake for about 10 minutes longer, until the cheese is melted and the pasta is tender.
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23
Let the baked pasta stand for 15 minutes.
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24
Garnish with the slivered parsley and serve.
