In a saucepan, combine sugar, flour and salt; stir in milk and mix well. Cook and stir over medium-high heat until mixture is thickened and bubbly. Cook and stir for 2 minutes longer. Remove from the heat. Stir in a small amount into egg yolks; return all to saucepan. Bring to a gentle boil. Cook and stir for 2 minutes; remove from heat. Add butter and vanilla; cool slightly. Slice the bananas into pastry shell; pour filling over top. Cool on wire rack for 1 hour. Store in the refrigerator. Before serving, garnish with whipped cream and bananas.