Place cold water in a small bowl and sprinkle gelatin over top. Set aside 5 minutes to soften. Place grated chocolate in a large heat-proof bowl. Pour boiling water over chocolate and stir until smooth. Stir gelatin mixture into chocolate mixture; stir until gelatin is completely dissolved.
In a small bowl, whisk egg yolks with 1/2 cup sugar until smooth and light. Whisk egg yolks into chocolate mixture, then stir in salt and vanilla extract. Allow mixture to cool.
In a large glass or metal mixing bowl, beat egg whites until foamy. Gradually add remaining 1/2 cup sugar, continuing to beat until whites form stiff peaks. Fold egg whites into cooled chocolate mixture. Spread into baked pastry shell and chill at least 2 hours, or until firm.
