Combine egg yolks, 1/2 cup sugar, salt, and nutmeg in top of a double boiler, beating well. Gradually add milk, stirring constantly. Bring water in bottom of double boiler to a boil. Cook over boiling water, stirring constantly, until mixture is thickened. Soften gelatin in cold water; add to hot mixture, stirring well. Stir in vanilla. Set mixture aside to cool.
Beat egg whites (at room temperature) until stiff peaks form. Fold into cooled gelatin mixture. Pour filling into pastry shell. Chill until firm.
Beat whipping cream until foamy; gradually add 2 tablespoons sugar, beating until soft peaks form. Spread whipped cream over filling. Sprinkle with grated chocolate.