Preheat your oven to 350°F (175°C). In a bowl, combine the graham cracker crumbs and melted butter. Mix until the crumbs are evenly coated.
Press the crumb mixture into the bottom and sides of a 9-inch pie dish to form the crust. Bake for 10 minutes, then set aside to cool.
In a medium saucepan, combine the mashed bananas, sugar, cornstarch, and salt. Gradually whisk in the milk until smooth.
In a separate bowl, whisk the egg yolks. Gradually add the banana mixture to the egg yolks, whisking constantly.
Place the saucepan over medium heat and cook the mixture, stirring constantly, until it thickens and comes to a boil.
Remove the saucepan from the heat and stir in the butter, vanilla extract, and ground cinnamon until well combined.
Pour the banana filling into the cooled graham cracker crust and smooth the top with a spatula.
Cover the pie with plastic wrap, ensuring the wrap touches the surface of the filling to prevent a skin from forming. Chill in the refrigerator for at least 4 hours or overnight.
In a mixing bowl, whip the heavy cream and powdered sugar until stiff peaks form.
Just before serving, spread the whipped cream over the chilled pie. Garnish with sliced bananas.
Slice and serve the banana cream pie, and enjoy!