In a medium saucepan, heat egg yolks; add milk. In a small bowl combine 1 cup brown sugar, flour and salt; stir to blend. Add the sugar and flour mixture to the milk mixture. Cook over medium heat, stirring constantly, until thick. Do not over cook. Add butter, vanilla, and 1 to 2 tablespoons brown sugar. Pour into a baked pie shell.
Make meringue. Beat egg whites until frothy. Add sugar and continue beating until stiff peaks form. Top butterscotch pie with the meringue and bake at 325° for 15 to 20 minutes, until browned.
Calories per serving: 374