Step 1 Heat the oven to 350 degrees. Toast the hazelnuts on a jellyroll pan until they're fragrant, 10 to 15 minutes. Place them in a kitchen towel and rub them briskly to remove the skins. Finely grind the nuts with the sugar in a food processor.
Step 2 Heat the cream to a simmer in a saucepan and remove it from the heat. Add the chocolate, stirring until it's melted and smooth. Stir in the nuts. Refrigerate the ganache, stirring occasionally, until it's cool but not firm, about 45 minutes.
Step 3Before filling the pears, whisk the ganache gently to aerate it until it thickens slightly and very soft peaks form.