If desired, the hazelnuts can be roasted at the same time as the chestnuts. Since the oven temperature is twenty-five degrees lower, you will need to add five to seven minutes to the roasting time of the hazelnuts.
Preheat oven to 350 degrees. Using a chestnut knife or a small paring knife, make an incision about 1/8 inch deep through the shell and into the flesh of each chestnut almost all the way around the circumference of the nut. Transfer to a chestnut pan or rimmed baking pan. Roast in the oven until the chestnuts are tender, about 35 minutes. Turn the oven off. Leaving the pan with the chestnuts in the oven, remove several at a time. Working quickly, place 1 chestnut in a towel, and, holding both, peel the chestnut while still hot. Remove and discard the shells and inner skin; set aside. Heat oven temperature to 375 degrees.
Place hazelnuts in a rimmed baking pan, and toast in the oven until golden, about 10 minutes. Remove from oven, place nuts in a clean towel, and vigorously rub between palms to release their skins. Roughly chop the nuts, and set aside. Tear frisee into large pieces, and transfer to a large bowl.
Melt butter in a medium skillet over medium-high heat. Add the pears and sugar, and cook until caramelized, 6 to 8 minutes. Remove from the pan, and transfer to a dish.
Cut pancetta into 1/2-inch dice. Place in the skillet, and cook until crisp, about 5 minutes. Remove from skillet, and transfer to paper towels to drain; set aside.
Return skillet with the pancetta fat to heat, and carefully add vinegar to pan. Raise heat to high, and cook, stirring, until reduced by about one-quarter, about 2 minutes. Add olive oil, and whisk to combine. Add chestnuts, adjust seasoning with salt and pepper, reduce heat to low, and simmer for 5 minutes. Add the reserved nuts, pears, and pancetta to the frisee. Pour the dressing and chestnuts over the salad, toss to combine, and serve.