Step 1Heat 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 2Heat 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.
Step 1Peel the pears, leaving the stems intact. Trim a thin slice off the bottom of each pear to give it a flat surface for standing upright on a plate. Using a paring knife or a melon baller, cut into the bottom of each pear and remove the core. Scoop out a small cavity in the center of each pear for the ganache filling.
Step 2Combine the wine, water, sugar, lemon juice, cinnamon stick and vanilla bean in a medium saucepan and bring them to a simmer, stirring occasionally to dissolve the sugar. Add the pears and simmer gently until tender when pierced with a knife, 25 to 30 minutes. Allow the pears to cool in the poaching liquid, then refrigerate until chilled, about 30 minutes.
Step 3Remove the pears from the liquid, reserving 2 cups for the sauce. Pat the pears dry with a paper towel and pipe or spoon the ganache into the center of the pears. Refrigerate the pears until the ganache is set, about 30 minutes.
Step 4Bring the 2 cups of reserved poaching liquid to a boil in a medium saucepan over high heat. Boil until the liquid is reduced to about 1 1/2 cups, about 5 minutes. To serve, stand a pear upright on a dessert plate and spoon a little sauce over it.