To make dulce de leche, place the unopened can of sweetened condensed milk in a saucepan, and add enough water to cover half-way up the can. Place the saucepan over medium-high heat and bring to a boil. Cook for 3 hours, adding more water as necessary. Remove from heat and cool.
Preheat oven to 350 degrees F (175 degrees C).
Combine the graham cracker crumbs with the butter in a mixing bowl until evenly blended. Press the crumb mixture evenly into a 9 inch pie plate.
Bake pie crust in preheated oven until lightly browned, 10-15 minutes. Remove from oven, and cool on a wire rack.
Open the can of dulce de leche, and pour half, or about 3/4 cup, over the pie crust. Slice the bananas and arrange half in a layer over the dulce de leche filling. Pour the remaining dulce de leche over the bananas. Top with remaining banana slices.
Pour the whipping cream into a mixing bowl, and beat until soft peaks form. Add the sugar and vanilla extract; continue beating until stiff peaks form. Spoon the whipped cream over the bananas. Chill at least 1 hour before serving.