Using two dull butter knives or a pastry blender, blend the flour, salt and shortening until the shortening is the size of peas.
6 tablespoons ice cold water
Fill a wide-mouthed glass with ice. Add water to the top. Measure or pour the ice cold water into the flour mixture. Using a spatula or your hands, mix the water into the flour to form a large ball of dough. You may need to add an extra tablespoon of water if you have excess flour. If you added too much water, add additional flour until the dough is well formed but not too sticky. Handle and mix the dough as little as possible.
Form dough into a disc and wrap in wax paper. Put wrapped dough in the freezer for 10 minutes or the refrigerator for 30 minutes.
Preheat oven to 325°F. Roll dough out onto a lightly floured surface. Place in a pie plate and gently crimp edges.
Place pie weights or a heavy lid from a saucepan on the bottom of the pie crust to hold it down. Par-bake at 325°F for 15 minutes so that dough can begin to set.
Remove from oven and set aside to cool slightly. Reduce oven heat to 325°F.
6 large eggs, separated into 4 eggs whites and 6 egg yolks
First, separate 4 eggs, reserving yolks in a small bowl for the lemon filling and egg whites in a large bowl for the meringue. Since we only need 4 egg whites for the meringue, discard the egg whites from the last two eggs but keep the yolks for the lemon filing. Set egg whites and eggs yolks aside.
3 lemons, cleaned
Zest three lemons with a grater. Reserve 1 tablespoon of zest and set aside. Juice lemons and strain juice, reserving ½ cup of lemon juice. Set aside.
1 cup sugar
¼ cup cornstarch
1/8 teaspoon table salt
1 ½ cups cold water
In a small sauce pan, stir together sugar, cornstarch, salt, and water. Heat over medium heat to a simmer, whisking frequently until mixture starts to thicken.
6 reserved egg yolks
When mixture starts to bubble and turn clear add egg yolks, two at a time, and whisk to combine.
reserved 1 tablespoon lemon zest
reserved ½ cup lemon juice
2 tablespoons butter
Add lemon zest, lemon juice, and butter to saucepan. Whisk to constantly to combine. Once returned to simmer, remove from heat and place one layer of plastic wrap on surface of filling to prevent a skin from forming.
⅓ cup cold water
1 tablespoon cornstarch
Combine water and cornstarch in a small saucepan. Heat over medium heat, whisking constantly, until mixture begins to thicken and turn translucent. Remove from heat and set aside.
reserved 4 egg whites
½ teaspoon vanilla extract
In a large bowl, beat egg whites and vanilla extract with an electric hand mixer on high until mixture is foamy.
½ cup sugar
¼ teaspoon cream of tartar
In a small bowl, combine sugar and cream of tartar. Add to egg white mixture, 1 tablespoon at a time, beating to combine until mixture forms soft peaks.
reserved cornstarch mixture
Add cornstarch mixture, 1 tablespoon at a time, beating to combine. Beat on high until stiff peaks form.
Assembly and Baking
Remove plastic wrap from filling and pour into par-baked pie shell. Spread evenly with a spatula.
Using a spatula, spoon meringue on top of filling by starting along the outer edge and working in. This ensures that the meringue won't sink into the center of the filling. Spread evenly with spatula, then use a spoon to form peaks along top of pie.
Bake at 325°F until meringue peaks have browned and and base surface of meringue has patches of golden brown, about 18 to 20 minutes.
Remove from oven and let cool to room temperature. Serve