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1
Heat oven to 350u00b0F with rack in middle.
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2
Roast hazelnuts on a baking sheet in oven until fragrant and pale golden inside (cut one open to test), 8 to 10 minutes (keep oven on). Wrap hot nuts in a towel and rub together to remove any loose skins. Halve nuts.
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3
While nuts are roasting, cook pancetta in a 9- to 10-inch heavy skillet over medium heat, stirring occasionally, until crisp. Transfer with a slotted spoon to paper towels to drain.
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4
Increase oven to 425u00b0F with rack in middle. Lightly oil baking sheet.
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5
Halve squash lengthwise and seed. Use vegetable peeler to peel squash into long thin ribbons into a large bowl. Toss squash with 2 tablespoons olive oil and 1/4 teaspoon each salt and pepper in a large bowl until coated. Spread ribbons evenly on a 13- by 9-inch baking sheet, or arrange ribbons into a 13- by 9-inch rectangle on a larger baking sheet. Bake until tender, 15 to 20 minutes, then turn on broiler and broil until lightly browned, 30 seconds to 1 minute.
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6
Bring cider to a boil in a small saucepan, then boil until reduced to 1/4 cup, about 5 minutes. Whisk reduced cider with cider vinegar, shallot, Dijon mustard, sugar, and 1/2 teaspoon salt in a medium bowl. Add 1/2 cup oil in a slow stream, whisking, and whisk until emulsified.
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7
Toss arugula and chicory in a very large bowl with about 1/2 cup vinaigrette (there will be some left over). Then toss in pancetta and hazelnuts.
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8
Cut squash into 8 rectangles and carefully transfer each with a metal spatula to a plate. Divide salad among plates and drizzle a little of remaining vinaigrette on squash.
