Preheat your oven to 425°F. Fit the bottom crust into a 9-inch pie plate and keep the top crust ready to roll; chilling the pastry briefly helps prevent shrinking during baking.

In a saucepan, blend 1/4 cup cornstarch with 1/4 cup of the water until smooth to avoid lumps.

Add 1-1/2 cups boiling water to the slurry and cook over medium heat, stirring constantly until the mixture thickens and becomes clear and glossy.

Remove from heat and stir in 1-1/2 cups sugar, 2 tablespoons grated lemon rind, and 1 tablespoon butter until melted and evenly incorporated. Allow this mixture to cool to room temperature.

Once the base is cool, stir the slightly beaten eggs into the filling, then add 1/4 cup lemon juice and mix until homogeneous.

Pour the prepared filling into the unbaked bottom pie shell, then place the top crust over and seal the edges tightly.

Brush the top crust with melted shortening, then with milk; lightly sprinkle flour over the entire top crust. Cut several vents into the top crust to allow steam to escape.

Bake for 10 minutes at 425°F to set and brown the top crust, then reduce heat to 375°F and bake for 30 minutes more, until the crust is golden and the filling is set.

Transfer the pie to a cooling rack for at least 2 hours before serving to allow the filling to fully set.