For the crust

1. Preheat oven to 350°F/177°C.  In a medium mixing bowl combine graham cracker crumbs, sugar, salt, and melted butter until evenly mixed.  Press crumb mixture evenly into a 10-inch tart pan with a removable bottom.  Bake crust for 10 minutes.  Allow to cool.

For the filling

1. Preheat oven to 425°F/218°C.  Pour the sweetened condensed milk into a pie dish.  Cover tightly with aluminum foil and place it into a larger roasting pan.  Fill with enough hot water to reach halfway up the pie dish.
2. Place onto the middle rack of the preheated oven for about 2 hours.  Check water level halfway through and additional hot water to replace any evaporated water.  At the 2 hour mark, check the condensed milk, it should have turned golden brown and thickened.  Remove from the oven and carefully transfer pie plate to a wire cooling rack.  Allow to cool to room temperture, uncovered.
3. Pour the cooled dulce de leche on top of the prepared crust and smooth with a small offset spatula.
4. Slice the bananas thinly and arrange them over the dulce de leche.

For the topping

1. In a large bowl using a hand-held mixer or stand mixer with the whisk attachment, whisk the heavy cream, powdered sugar and vanilla on medium-low speed until mixture becomes frothy.  Increase speed to medium-high and continue whisking until medium peaks form, about 3 minutes.  Careful not to over mix or else it will become thick and lumpy.
2. Immediately spread the whipped cream over the banana layer.
3. Refrigerate the pie for at least 2 hours before serving.