Prepare and chill the 9-inch baked pastry shell.

In a 4-cup microwave-safe measuring cup, combine 3/4 cup sugar, 1/4 cup cornstarch, 1/2 teaspoon salt, and 1 1/2 cups water.

Microwave on high for 5-6 minutes, stirring 2-3 times until the mixture thickens.

Gradually whisk a small amount of the hot mixture into the separated egg yolks, then blend the warmed yolks into the remaining hot mixture.

Microwave for 1 minute, then stir in 2 tablespoons of butter, 2 teaspoons of grated lemon peel, and 1/3 cup of lemon juice.

Pour the lemon filling into the prepared pastry shell.

Preheat the oven to 350 degrees Fahrenheit.

In a clean bowl, beat the 3 egg whites with 1/4 teaspoon of cream of tartar until frothy.

Gradually add 1/4 cup of sugar, beating until soft peaks form.

Spoon the meringue over the lemon filling, carefully spreading it to seal the edges and cover the entire filling.

Bake for 10-12 minutes, or until the meringue is golden brown.

Let the pie cool completely before serving.