In a small saucepan, whisk together the sugar, corn starch, and water.
Place the saucepan on medium heat and bring to a boil, constantly stirring the mixture.
Boil the mixture, constantly stirring, until it thickens.
Remove the saucepan from the heat, and allow the mixture to cool.
Meanwhile, separate your eggs; you'll need 3 egg whites.
Beat those egg whites in a mixing bowl until they begin to form peaks.
Add the cooled sugar mixture and the cream of tartar to the stiffly beaten egg whites, and beat some more, until your meringue begins to form stiff peaks.
Spread the meringue all over the top of your pie, making sure to spread it all the way up to the edges of your pie.
At this point, you can form curls with a spoon if you want... I just used my spatula to kinda form a few little curls and left it with a somewhat wavy appearance.
Bake your pie for at least 15 minutes at 350°, maybe a little longer to ensure that your meringue is cooked through. It will start to turn golden.
Remove from the oven and allow to cool on a wire rack for about an hour. Then refrigerate for at least 2 to 3 hours before serving.