Preheat oven to 350°F (177°C).
Make the crust: If you’re starting out with full graham crackers, use a food processor or blender to grind them into fine crumbs. Stir the graham cracker crumbs and granulated sugar together in a medium bowl, and then stir in the melted butter. The mixture will be thick, coarse, and sandy. Try to smash/break up any large chunks. Pour the mixture into an ungreased 9-inch pie dish. With medium pressure using your hand, pat the crumbs down into the bottom and up the sides to make a compact crust. Do not pack down with heavy force because that makes the crust too hard. Simply pat down until the mixture is no longer crumby/crumbly.
Bake the crust for 15 minutes. Cool for 15 minutes.
For the whipped cream: Using a hand mixer or a stand mixer fitted with a whisk attachment, whip the heavy cream, sugar, and vanilla extract on medium-high speed until medium peaks form, about 3-4 minutes.
Spread dulce de leche on top of the crust. Arrange banana slices in 1–2 layers on top of the dulce de leche, then spread whipped cream on top.
Refrigerate pie uncovered for at least 2 hours and up to 1 day. Garnish with toppings before serving, if desired.
Cover and store leftover pie in the refrigerator for up to 5 days.
