In a 9-inch pie dish, bake pie crust at 450F for 10 minutes, or until golden brown. Set aside to cool.
Turn oven down to 400F. In a double boiler, mix sugar, cornstarch, and salt. Stir in hot water and combine until smooth. Add crumbs and continue mixing until smooth and thickened.
In a small bowl, beat egg yolks, and add a small amount of the mixture. Stir and then add it to the rest of the mixture. Cook over low to medium heat for 2 minutes. Add butter, lemon zest, and juice. Allow to cool slightly.
Make the meringue: beat egg whites with salt until frothy. Gradually add cream of tartar and sugar. Beat until stiff.
Pour the filling into the pre-baked shell. Pile meringue on top and cover the filling completely. Bake for 10 minutes or until lightly browned.