Start by pre-baking the pie crust. If you use an all butter pie crust recipe, it will shrink as it cooks. To minimize shrinking, cook crust upside down. Set in pie dish and set another pie dish on top. Invert onto a baking sheet lined with parchment paper. Bake in 375 degree preheated oven for 20 minutes. Remove from oven, turn pie dish right side up, remove top pie dish, poke crust several times with fork, and continue cooking for 15-20 minutes. Remove from oven.
Reduce oven temperature to 350 degrees F.
Meanwhile, make the lemon filling.
Using a stand mixer, cream the butter until smooth and fluffy. Beat in the sugar and lemon zest and blend until smooth, scraping sides down half way through.
On low speed, add the egg yolks one at a time. Then add the lemon juice and corn starch. Mix until combined.
Add about 1/2 inch of water to a pan and set a non-reactive metal bowl on top. You want a double boiler set up so that the steam from the water cooks the lemon curd; not direct heat.
Add the lemon mixture to the bowl and heat the water so that it boils, whisking the lemon mixture the entire time. Be sure to use an instant read thermometer. The curd should thicken around 170 degrees F, after about 10 minutes of cooking and whisking. Pour filling onto cooked pie crust.
To make the meringue topping, whisk egg whites on medium high speed until foamy. Whisk in cream of tarter. Gradually add sugar while mixer is running, and continue to whip until soft, or semi-stiff, peaks form. Do not over beat or they will break. Spread meringue topping over hot pie filling and be sure to create a seal all the way around the crust, otherwise it will pull away when you bake it. You can spread the topping evenly, or you can make it more decorative by swirling in peaks and valleys.
Bake pie in 350 degrees F preheated oven until golden brown, 10-12 minutes.
Allow pie to cool at room temperature. Best if served that day. Pie can be stored in refrigerator 2-3 days, however the meringue may begin to weep causing moisture to accumulate.