In a medium saucepan over high heat, combine the water and sugar and bring to a boil. Stir to dissolve the sugar. Add the vanilla bean, lemon zest, and ginger. Reduce the heat to low and simmer the syrup for 10 minutes. Add the lemon juice and pears (and vanilla extract, if using). Cover and poach gently until the pears are soft, about 15 minutes. Refrigerate the pears in the liquid for at least 2 and up to 24 hours. Put the raisins in a small bowl, cover with the Cognac, and also let soak in the refrigerator for the same amount of time.
Heat the oven to 325°F. On a small baking sheet, toast the almonds until they're golden brown in the center, about 12 minutes. Let cool, chop coarsely, and set aside.
Increase the heat to 400°F. Set the pears in a colander to drain (it's okay to discard the syrup).
Put a clean, damp (but not wet) dishtowel on the counter and gently lay the phyllo sheets on top. Cover with a second damp towel (this will keep the pastry from drying out). Cover you workspace with a piece of parchment slightly larger than the phyllo sheets. Remove two phyllo sheets and lay them on top of the parchment with the longest side facing you. Brush generously with melted butter, and sprinkle with half the toasted, chopped almonds. Lay the other two phyllo sheets on top and repeat.
Sprinkle the Amaretti crumbs or breadcrumbs in a band about 2 inches wide along the edge closest to you. Arrange the pears on top of the crumbs and sprinkle with the raisins.
Starting at the edge closest to you and using the parchment as an aid, gently roll up the strudel and set it on a parchment-lined baking sheet. With a serrated knife, score the top of the strudel at about 2-inch intervals. Bake on the middle rack of the oven for 20 minutes. Lower temperature to 350°F and continue to bake until the pastry is a deep golden brown, 10 to 15 minutes. Let cool and store at room temperature until ready to serve.
To serve, reheat in a 350°F oven until warm and then sprinkle with the confectioners' sugar.