Prepare pie crust according to package directions, if using a store bought product. Poke a few holes in the crust to prevent shrinkage before baking. Let pie crust cool.
In a saucepan, add sugar, flour and salt.
Stir in milk and mix well.
Cook over medium-high heat until mixture is thickened and starts to bubble.. this could take up to 15 minutes.
Cook and stir for 2 minutes longer.
Remove from the heat.
Stir a small amount into egg yolks to help temper the eggs; return all to saucepan.
Bring to a gentle boil.
Cook and stir constantly for 2 minutes.
Remove from the heat.
Add butter and vanilla; cool slightly.
Slice your bananas and add one layer of bananas to the bottom of your baked and cooled pie crust; pour filling over top of bananas.
Top with remaining bananas.
Cool on wire rack for 1 hour.
Store in the refrigerator, covered lightly with plastic wrap so a film doesn't develop over custard, until chilled, about 4 hours.
Before serving, top with leftover bananas and cool whip/whipped cream.