FOR THE CRUST:
1. Set a rack in the middle of the oven and preheat the oven to 350ºF.
2. In a medium mixing bowl, stir together the graham cracker crumbs, sugar, salt, and melted butter until well blended. Press evenly over the bottom and up the sides of a 9-inch pie pan. Bake, rotating the pan halfway through, until dry to the touch, 8 to 10 minutes. Remove from the oven and set aside to cool.
FOR THE FILLING:
3. In a medium saucepan, combine the sugar and cornstarch. Add the half-and-half and egg yolks and whisk until well combined. Bring to a boil over medium heat, stirring continuously, and boil for 1 minute, then remove from the heat. Stir in the butter and vanilla.
4. Pour half the filling into the cooled crust.
5. Slice 2 of the bananas and cover the filling in the crust with the banana slices. Pour the remaining filling over the bananas. Cover with plastic wrap, pressing it directly against the filling to keep a skin from forming. Chill for at least 3 hours or up to overnight.
6. Slice the 2 remaining bananas and arrange them over the filling, reserving a few slices for garnish.
FOR THE WHIPPED CREAM:
7. Place the bowl and whisk attachment of a stand mixer (or a large metal bowl and a whisk, or beaters for a handheld mixer) in the freezer for at least 20 minutes.
8. Place the heavy cream, sugar, and vanilla in the chilled bowl and beat on low speed for 30 seconds, then increase the speed to medium and beat for an additional 30 seconds. Increase the speed to high and beat until the cream has doubled in volume and stiff peaks form, an additional 1 to 2 minutes. (The whipped cream can be prepared ahead, tightly covered with plastic wrap, and stored in the refrigerator for up to 1 day. If the cream separates, whip it again to reincorporate the liquid.)
9. Spread the whipped cream over the bananas and garnish the center of the pie with the reserved banana slices.
FOR THE CHOCOLATE SAUCE (OPTIONAL):
10. In a small heavy-bottomed saucepan over medium heat, heat the half-and-half and butter until small bubbles begin to form around the edge of the pan, 3 to 4 minutes (do not allow the cream to boil). Remove the pan from the heat.
11. Place the chocolate chips and vanilla in a medium heatproof bowl, add the hot half-and-half mixture, and let it rest for 2 minutes. Whisk until creamy.
12. Pour the chocolate sauce into a pastry bag (or a plastic bag with a small hole in one corner) and pipe swirls of chocolate over the top of the pie.