Combine milk, cream, sugar and salt in medium saucepan over medium-low heat. Whisk until sugar is dissolved.
In a 2-cup pyrex measuring cup, whisk together egg yolks and cornstarch.
Continue whisking egg while slowly pouring in 1 cup of hot milk mixture. This warms the eggs without cooking them.
Slowly pour the egg mixture back into the milk while whisking continuously. Increase heat if needed, whisk until mixture thickens and big bubbles begin to pop on the surface, 1-2 minutes.
Remove from heat. Add butter and vanilla.
Pour custard filling into a bowl. Cover with waxed paper and cool for 15 minutes.
ASSEMBLE PIE
Slice bananas, not too thin, and arrange in an overlapping pattern on bottom of the piecrust. Reserve some slices for garnish.
Pour filling over the bananas and smooth the top. Cover with the waxed paper to prevent a skin from forming. Refrigerate at least 4 hours or overnight.
Just before serving beat cream. Add icing sugar and vanilla. Beat just until stiff peaks form.
Pile whipped cream in center of pie and garnish with banana slices.