Step #1 TO MAKE FILLING: Mix flour & constarch with 1/3 c cold milk to make a thin smooth paste, & set aside.
Step #2 In a separate bowl, beat egg yolks, then add sugar & salt & beat well.
Step #3 In a medium saucepan, scald remaining milk, stirring constantly.
Step #4 While you continue stirring the milk in the pot, add a small amount of the scalded milk to the flour paste & a small amount to the egg/sugar mixture.
Step #5 Pour both mixtures into the pot with the scalded milk & stir well.
Step #6 Cook over med-heat/flame, stirring constantly, until thickened.
Step #7 Remove from heat.
Step #8 Add butter & vanilla, & stir well.
Step #9 TO ASSEMBLE PIE: Pour a layer of custard filling in in the pie shell.
Step #10 Place a layer of sliced bananas on top of the filling, then repeat with custard & bananas, & ending with a final top layer of custard.