Set heavy 12-inch skillet over medium heat. Pour in hazelnuts. Cook, shaking the pan occasionally, until skins have turned dark brown in spots and begun to split, about 15 minutes. While hot, carefully pour hazelnuts into center of clean dishtowel. Rub together to remove skins. When hazelnuts are cool enough to handle, finely chop and set aside.
Wipe out skillet to remove any hazelnut bits. Set over medium-high heat. Add butter and cook until bubbly and beginning to turn brown. Reduce heat to medium. Add cauliflower, sage, chopped hazelnuts, and a few generous pinches of salt and pepper and cook, stirring occasionally, until cauliflower is tender and has caramelized in spots, 10 to 15 minutes. Depending on how well your pan retains heat, you may find the nuts are in danger of burning before the cauliflower becomes tender. If that's the case, pour in a couple of tablespoons of water, cover the pan and reduce heat to low, cooking until cauliflower is tender, then proceed.
Quarter and core pear and slice thinly. Add pear and parsley to cauliflower mixture, stir to distribute, and taste for seasoning. Serve warm.