In a medium saucepan, whisk together sugar, cornstarch, and salt.
Gradually add milk while whisking until smooth.
Cook over medium heat, stirring constantly until the mixture thickens.
Remove from heat and whisk in egg yolks, butter, and vanilla.
Slice 2 bananas and arrange them on the bottom of the pie crust.
Pour the custard mixture over the bananas, spreading evenly.
Cover the surface with plastic wrap to prevent a skin from forming.
Chill in the refrigerator for at least 4 hours, or until set.
Whip the heavy cream with powdered sugar until soft peaks form.
Spread the whipped cream over the chilled pie and garnish with banana slices.