How to Make It
To prepare the filling, combine first 5 ingredients in a saucepan. Add 1 cup water, stirring constantly with a whisk. Bring to a simmer over medium heat, and cook 5 minutes, stirring frequently. Stir in butter, and remove from heat. Stir in lemon juice. Add egg yolks, 1 at a time, beating well after each addition. Place pan over low heat; cook 3 minutes, stirring constantly. Spoon filling into crust. Cool to room temperature.
To prepare the meringue, place the egg whites and cream of tartar in a large bowl; beat with a mixer at high speed until foamy. Combine 2/3 cup sugar and 1/4 cup water in a small saucepan; bring to boil. Cook mixture, without stirring, until candy thermometer registers 238°. Pour hot sugar syrup in a thin stream over egg white mixture, beating at high speed until stiff peaks form. Spread the meringue evenly over filling, and seal to edge of crust.
Broil meringue for 1 minute or until lightly browned; cool pie on wire rack. Chill until set.