Combine the flour, salt and shortening in a large mixing bowl, and cut in the shortening until the mixture resembles coarse meal. With a fork, stir in only enough ice water to enable the dough to be gathered into a ball. Flatten the ball into a disk, wrap in waxed paper and refrigerate for at least 1 hour. On a lightly floured surface, roll out the pastry into an 11-inch round. Without stretching, fit the pastry into a 9-inch pan. Trim, leaving a 1/2-inch overhang all around; discard the pastry scraps or reserve for another purpose. Tuck under the excess pastry and crimp to make a decorative edge. Refrigerate for 30 minutes before baking. Preheat the oven to 425 F. Line the pastry with aluminum foil and weigh down with aluminum pie weights or dried beans to prevent the pastry from bubbling. Bake for 15 to 20 minutes, or until crisp and golden. Cool on a rack. Prepare The Filling: In a large mixing bowl, combine the cornstarch, flour, sugar and salt. Stirring constantly, pour in the boiling water nad blend until smooth. Add the egg yolks and orange juice and beat until smooth. Transfer the filling to the top of a double boiler over, but not touching, boiling water and cook, stirring frequently, for 15 to 20 minutes. When the mixture is very thick, remove it from the heat. Add the butter, orange zest, lemon juice and grenadine; stir until the butter melts. Cover with a round of waxed paper place directly on the surface and let the filling cool to room temperature. Pour into the pre-baked pie shell, cover with waxed paper and chill for at least 5 hours or overnight. Prepare The Meringue: Preheat the oven to 350 F. Place the egg whites in a bowl, add the salt and beat until the whites are foamy. Add the cream of tartar and beat until soft peaks form. Gradually add the sugar and continue beating until the whites are stiff and very glossy. Do no overbeat or the meringue will be dry. Pile the meringue on the filling, mounding it in the center and spreading it out to the edge of the crust to seal well. Bake in the center of the oven for 15 minutes, or until the meringue is golden. Let cool and chill for 3 hours before serving. To slice neatly, use a knife dipped into boiling water before making each cut.