Whisk the sugar, salt and cornstarch together thoroughly in a medium saucepan.

Add the water, lemon juice and zest, blending well.

Whisk in the egg yolks.

Keep whisking until there are no yellow streaks.

Add butter.

Stir constantly with a wooden spoon.

Bring mixture to a simmer over medium heat.

Then cook for 1 minute. The filling should be very thick (like pudding).

Pour the filling in the pie crust and top with Meringue (directions below).

Bake for 20 minutes at 350F degrees or place the pie under the broiler (on high) for about 5 minutes until the meringue is nicely browned. Watch it carefully so it doesn't burn.

In a separate bowl, beat egg whites and cream of tartar on high until soft peaks form.

Gradually beat in the sugar until the peaks are stiff but not dry.

Add the vanilla and beat until combined.

Immediately spread the Meringue Topping over the pie and bake as noted above.