Combine egg whites and salt in a mixing bowl; beat until foamy. Gradually add 1/4 cup plus 2 Tbsp sugar, 1 Tbsp at a time, and vanilla, beating until stiff peaks form. Set aside.
Combine 1 cup sugar and cornstarch in a heavy saucepan. Beat egg yolks lightly in a small bowl; add milk. Add yolk mixture to sugar mixture in saucepan; stir well. Cook over medium heat, stirring constantly, until mixture comes to a boil. Boil 1 minute, stirring constantly. Remove from heat; stir in toasted pecans and butter.
Pour into pastry shell. Spread meringue over warm filling, sealing to edge of pastry. Bake at 400 degrees F for 8 minutes or until lightly browned. Garnish with sliced pecans, if desired. Cool before serving.