Separate the egg yolks from egg whites. Place whites in a large mixing bowl and allow them to stand at room temperature for 30 minutes. Place yolks in a small mixing bowl; set aside.

For filling: In a medium saucepan, stir together powdered sugar, cornstarch, and salt. Gradually stir in milk and peanut butter. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Remove from heat.

Slightly beat egg yolks with a rotary beater or fork. Gradually stir about 1 cup of the hot mixture into egg yolks. Pour egg yolk mixture back into filling in saucepan. Bring to a gentle boil. Cook and stir 2 minutes more.

Remove from heat. Stir in 1 teaspoon of the vanilla. Keep the filling warm while preparing the meringue.

For meringue*: Add the remaining 1/2 teaspoon vanilla and the cream of tartar to the egg whites. Beat with an electric mixer on medium speed for about 1 minute or until soft peaks form (tips curl). Add the granulated sugar 1 tablespoon at a time, beating on high speed for about 4 minutes or until mixture forms stiff, glossy peaks (tips stand straight) and sugar dissolves.

Pour warm filling into piecrust. Immediately spread meringue over warm pie filling, carefully sealing to edge of pastry to prevent shrinkage. Bake in a 350 degree F oven for 15 minutes. Cool on a wire rack for 1 hour. Chill 3 to 6 hours before serving. Makes 8 servings.

Omit the meringue, if you like. Pour hot filling into baked pastry shell and chill for 4 to 6 hours. Just before serving, spread with some sweetened whipped cream.