Preheat oven to 375 F.

Place the egg yolks in medium size mixing bowl and set aside. In a medium saucepan, combine cornstarch, water, sugar and salt. Whisk to combine. Then turn stove top on medium heat. Bring mixture to a boil, making sure to stir frequently, and allow it to boil for 1 to 2 minutes.

Remove the sugar and water mixture from the heat and gradually add the hot mixture to the egg yolks and stir until they are incorporated together in a smooth mixture. Then return the egg-sugar-water mixture to the same saucepan and turn the heat down to low. Cook, stirring constantly, for 1 to 2 more minutes.

Remove from heat and gently stir in butter, lemon juice and zest until well combined. This may look broken, but just keep stirring until everything is beautiful and incorporated.

Pour this amazing mixture into the pie shell and proceed to make the meringue.

Place the egg whites and cream of tartar in the bowl of a stand mixer fitted with the whisk attachment. Beat the egg whites until soft peaks form and then gradually add the sugar and continue beating until stiff peaks form, approximately 2 to 3 minutes. The stiffer the better for an amazing meringue pie crust.

Top lemon filling with your meringue that's already in the pie shell. Make sure to top with meringue while filling is still hot, it helps to stick together better. Also, make sure the meringue completely covers the filling and make sure that it goes right up to the edge of the crust.

Bake the pie for 8 to 12 minutes or until meringue is golden. Remove from oven and cool on a wire rack or in your fridge. Make sure pie is completely cool before slicing.