Position a rack in the middle of the oven. Heat the oven to 350 degrees F. Press the pie dough into the edges around the pan and trim any excess dough. Press the edges of the dough over the lip of the pan. Refrigerate for 15 minutes.
Poke holes using a fork around sides and into the bottom of the dough (this is what pastry pros call 'docking'). Place a large piece of parchment paper on top of dough and fill with dry beans. Press beans into edges of dough, set on a half sheet pan, and bake in the oven for 15 minutes, or until the edges are golden. Remove parchment and beans and continue baking until golden brown in color, approximately 10 minutes longer. Remove from oven and place on cooling rack. Allow to cool completely while preparing the filling.
Crank the oven to 375 degrees F. Whisk the egg yolks in a medium mixing bowl and set aside.
Whisk together cornstarch, sugar and salt in a medium saucepan (this will eliminate any clumps in the cornstarch). Add the water, lemon juice, butter and lemon zest. Bring mixture to a simmer, stirring gently, over medium heat. Remove from heat. One whisk full at a time, add the cornstarch mixture to egg yolks and stir until you have added at least half of the cornstarch mixture.
Return the all of the egg-starch mixture to saucepan, turn heat down to low and cook, stirring gently, for one more minute. Pour mixture into pie shell. The filling should be very thick going into the crust. If there‚Äôs any doubt in your mind that your filling isn't cooked enough ‚Äì stick a spoonful on a plate and stick it into the fridge for 2 minutes. The consistency should be similar to mayonnaise.
Combine the egg whites and cream of tartar in bowl of stand mixer with whisk attachment. Beat egg whites until soft peaks form and then gradually add the sugar and continue beating until stiff peaks form, approximately 2 minutes. Top with the pie meringue while lemon filling is still hot.
Make sure meringue completely covers the filling and connects right up to the edge of the crust. Bake for 10 to 12 minutes or until meringue is golden. Remove from oven and cool on cooling rack. Make sure pie is cooled completely before slicing, this will take approximately 4 to 6 hours.
Place egg whites and cream of tartar in bowl of stand mixer with whisk attachment. Beat egg whites until soft peaks form and then gradually add sugar and continue beating until stiff peaks form. Approximately 1 to 2 minutes. Use to top lemon filling.