Preheat the oven to 375°F. Let the pie crust sit out at room temperature for 20 minutes, then unroll the crust and fit it into an 8 or 9-inch pie pan with the parchment on top. Prick the pie crust with a fork in a number of places. Remove the parchment (reserve it!) and crimp the edges decoratively. Fit the parchment back into the pie crust and fill the pie with dried rice, dried beans, or pie weights. For more on blind baking a pie crust click here.
Bake on the lower rack of the oven for 20 minutes, then remove from the oven, carefully remove the parchment and weights, and return the crust to the oven. Bake for another 15 to 20 minutes until golden and cooked through. Set on a cooling rack to cool completely.
Meanwhile, in a large saucepan, whisk together the sugar, cornstarch, salt and milk . Place the pan over medium-high heat until it starts to bubble and thicken, then reduce the heat a bit so that it bubbles slowly for another two or three minutes and thickens up further.
Lightly beat the egg yolks in a small bowl. Slowly pour a few tablespoons of the hot filling into the egg yolks, whisking all the while, until blended. Slowly pour this egg mixture back into the pan over medium-high heat, whisking constantly, so that it is all smooth and blended. Allow to come to a boil ( big bloopy bubbles will rise to the top and pop) and stir for another 2 minutes until the mixture is quite thick.
Remove from the heat and add the butter and vanilla. Stir until the butter is melted. Transfer to a container and place some plastic wrap directly on the surfaced of the custard. Refrigerate the mixture for about 1 hour, until it is fairly cool and evenly thicker.
When the crust and the custard are cooled to at least room temperature, slice the bananas about 1/2 -inch thick. Distribute the bananas on the bottom of the pie crust. Carefully dollop over the custard and use the back of a spoon or an offset spatula to smooth the top.
Use a spoon or a piping bag to cover the top of the pie with the whipped cream. If you used a spoon, then use the back of a spoon or an offset spatula again to make nice swirly swoops in the whipped cream. Refrigerate the pie for 4 to 6 hours, until fully chilled. Top the pie with chocolate curls if desired: Use a vegetable peeler to scrape down the side of the chocolate bar, so that thin pieces of the chocolate fall off in curls.
Slice and serve.
Notes
The custard is made by thickening a sweetened milk mixture on the stove. Then, a small amount of the hot mixture is whisked quickly into the eggs so they don’t scramble. This is called tempering - because you are bringing the eggs up to a higher temperature, closer to the temperature of the custard, before you add them in.