Mix dry ingredients (cornstarch, flour, & salt) in small bowl
In a large sauce pan, scald 1 cup milk & then mix in brown sugar
Add dry ingredients to milk & brown sugar mixture
Boil for 1 minute
Remove from heat
In a separate bowl, mix one half of the hot mixture into 3 slightly beaten egg yolks & add 6 tbsp butter
Bring mixture to boil for 1 more minute
Remove from heat & add 1 tsp vanilla
Cool filling by stirring occasionally.
Pour cooled mixture into cooled baked pie shell and refrigerate.
When completely cooled, top with meringue, cool whip or whipped cream & butterscotch chips