Place egg whites in a small mixing bowl; let stand at room temperature for 30 minutes. Meanwhile in a large saucepan, combine the pudding mix, milk and sour cream until smooth. Cook and stir over medium heat until thickened and bubbly, about 5 minutes. Reduce heat; cook and stir 2 minutes longer.
Remove from the heat. Gradually whisk 1 cup hot filling into egg yolks; return all to the pan, Bring to a gentle boil; cook and stir for 2 minutes. Remove from the heat, Gently stir in lemonade concentrate, keep warm.
Add lemon juice, and cream of tartar to egg whites; beat on medium speed until soft peaks form. Gradually beat in sugar 1 tablespoon at a time, on high until stiff glossy peaks form and sugar is dissolved.
Pour warm filling into pie crust, Spread meringue over filling, sealing edges to crust. Bake at 350* for 15-20 minutes or until meringue is golden brown.Cool on a wire rack for 1 hour. Refrigerate for at least 3 hours before serving. Enjoy!