Preheat the oven to 325°F.
For the crust: In a small bowl, combine the gingersnap crumbs, butter and granulated sugar. Press the crumb mixture into the bottom and up the sides of a 9-inch pie pan. Bake for 6 minutes. Let cool on a wire rack.
For the filling: In a small bowl, combine the gelatin and 1/2 cup cool water and let sit for 5 minutes until the gelatin softens and blooms.
In a medium saucepan over medium-high heat, bring the milk, cocoa powder, 1/4 cup granulated sugar and the salt to a simmer, stirring constantly. Remove from the heat and add the gelatin mixture, stirring until the gelatin is completely dissolved.
Put the egg yolks in a medium bowl and beat lightly. Gradually, in a slow stream, add 1/4 cup of the chocolate mixture to the egg yolks while whisking constantly. Pour the chocolate-yolk mixture into the pan with the remaining chocolate mixture. Cook over medium heat, stirring constantly, until slightly thickened, about 8 minutes. Let cool until barely warm, about 20 minutes.
In a large bowl using an electric mixer, whip the egg whites to soft peaks. Add the remaining 2 tablespoons granulated sugar and the vanilla and whip to stiff peaks. Gently fold the cooled chocolate mixture into the meringue in three additions.
Spoon the chocolate mixture into the cooled pie crust. Cover and refrigerate for 2 hours.
For the topping: Whip the cream with the confectioners' sugar in a bowl. Place dollops of whipped cream on the pie and grate the chocolate on top, if desired.