Combine first 3 ingredients. Press into a 9-inch pieplate.
Bake piecrust at 350° for 10 minutes or until lightly browned; cool.
Stir together sweetened condensed milk and lime juice until blended. Pour into prepared crust. Set aside.
Beat egg whites and cream of tartar at high speed with an electric mixer just until foamy.
Add granulated sugar gradually, 1 tablespoon at a time, beating until soft peaks form and sugar dissolves (2 to 4 minutes).
Spread meringue over filling.
Bake at 325° for 25 to 28 minutes. Chill 8 hours.
*Bottled Key lime juice may be substituted for fresh juice.