Preheat oven to 400 degrees.

To make lemon filling:

In medium saucepan, combine cornstarch, flour, sugar, and salt, mixing well.

Gradually add 2 cups water, stirring until smooth.

Over medium heat, bring to boiling, stirring occasionally; boil 1 minute.

Remove from heat.

Quickly stir some of hot mixture into egg yolks. Return to hot mixture; stir to blend.

Return to heat; cook over low heat 5 minutes, stirring occasionally.

Remove from heat. Stir in lemon juice, lemon peel, and butter.

Pour into baked pie shell.

To make meringue:

In medium bowl, with mixer at medium speed, beat egg whites with cream of tartar until frothy.

Gradually beat in sugar, 2 tbsp at a time, beating after each addition.

Then beat at high speed until stiff peaks form when beater is slowly raised.

Spread over lemon filling, carefully sealing to the edge of the crust and swirling top decoratively.

Bake 7-9 minutes, or until the meringue is golden-brown.

Let pie cool completely on wire rack, 2 1/2 to 3 hours. Refrigerate.