1. Preheat oven to 375°F.

2. In a medium saucepan, whisk together cornstarch, sugar, and salt.

3. Gradually whisk in milk until smooth.

4. Over medium heat, bring to a low simmer, stirring constantly.

5. In a small bowl, whisk egg yolks.

6. Slowly add a few ladles of the hot milk mixture, whisking constantly.

7. Pour egg yolk mixture into the saucepan and continue to cook, stirring constantly, until mixture is thick and bubbly.

8. Remove from heat and stir in butter and vanilla extract.

9. Pour into the graham cracker crust and top with sliced bananas.

10. In a small bowl, whip the heavy cream until soft peaks form.

11. Gradually add the powdered sugar while continuing to whip until stiff peaks form.

12. Spread whipped cream over the top of the pie.

13. Refrigerate for at least 3 hours before serving.