In a double boiler, whisk together the brown sugar, flour, and cornstarch.
Add just enough milk to make a paste.
Mix in beaten egg yolks, and then add the remainder of the milk.
Cook slowly, stirring constantly; when thick, remove from heat.
Add butter or margarine and 1 teaspoon vanilla.
Pour the filling into the baked pie shell.
In medium mixing bowl, beat egg whites until stiff.
Beat in cream of tarter, white sugar, and 1 teaspoon vanilla.
Spread meringue over pie filling.
Bake at 375 degree F (190 degrees C) until meringue peaks turn a golden brown.