• Preheat oven to 350°F.
• In the bowl of a food processor pulse graham crackers and sugar until finely ground. Add butter and pulse until moistened. Use the bottom of a measuring cup, glass, or ramekin to press crust mixture into the bottom and up the sides of a 9-inch pie plate. Bake until fragrant and golden brown, about 12 minutes.
• Cool completely on a wire rack. Refrigerate while preparing filling.

For the filling:

• In a medium heatproof bowl, whisk together sugar, flour, cornstarch, salt and eggs until very smooth.
• In a medium saucepan, bring milk just to a boil. Gradually add hot milk to the egg mixture, whisking constantly. Return egg and milk mixture back to saucepan. Cook over medium heat, stirring constantly, until it begins to boil and thickens.
• Remove from heat and stir in butter and vanilla.
• Spread dulce de leche on top of the chilled crust. Spread banana slices over dulce de leche in an even layer. Spoon the warm milk mixture over bananas. Cover with plastic wrap and refrigerate until completely set, at least 6 hours.

For the topping:

• Before serving, place cream in a bowl and whip with an electric mixer fitted with the whisk attachment. Whip until thickened, then add in powdered sugar and cinnamon. Continue whipping until stiff peaks form.
• Spread over chilled pie. Drizzle with as much dulce de leche as you like. You may need to microwave it until warmed and pourable before drizzling.
• Serve cold the day the pie is topped with whipped cream. To make cutting slices easier, pop the pie in the freezer for 30 minutes before serving.