Make the crust: In a medium bowl, mix together the wafer crumbs, granulated sugar, butter, salt and pistachios. Pour the crust mixture into a 9-inch pie plate and use the bottom of a lowball glass or measuring cup to press evenly along the bottom and sides. Freeze for 10 minutes. Meanwhile, heat oven to 350 degrees.

Bake the crust for 15 minutes, until it begins to turn a slightly deeper golden brown. Cool completely.

Make the pudding: In a small bowl, whisk together the egg yolks and cornstarch until thickened. Set aside close to the stove. In a heavy saucepan, heat the brown sugar and 2 tablespoons of water over medium until the sugar dissolves, stirring occasionally. Bring to a boil and continue to cook for 4 to 6 minutes, until the bubbling slows. (It should reach about 240 degrees on an instant-read thermometer; be careful not to burn it). Turn off the heat, and add the cream and milk carefully as they will bubble vigorously at first. Whisk thoroughly. You may have some bits of undissolved sugar, but they will continue to melt.

Return to medium heat and cook the cream mixture until it begins to simmer, an additional 3 to 5 minutes. Carefully and slowly pour about ¼ cup of the hot cream into the yolk mixture, whisking constantly. Pour the yolk mixture into the saucepan while whisking, then continue to cook, whisking continuously, until large bubbles form on the surface. Remove from the heat, then whisk in the butter, rum and salt. Taste the pudding and stir in more salt if you’d like.

Layer half of the banana slices over the bottom of the cooled crust. Pour the warm pudding over the bananas and smooth out the top. Place the remaining bananas on top, cover loosely with plastic wrap so a skin doesn’t form and let cool at room temperature for about 30 minutes. Chill the pie completely, for at least 4 hours or overnight.

Make the whipped cream: Use a hand mixer and a large bowl or a stand mixer fitted with a whisk attachment to beat the crème fraîche and heavy cream on high speed until medium-stiff peaks form, 2 to 3 minutes. Add the powdered sugar and rum and beat until just incorporated. Dollop the whipped cream on top of the chilled pie, top with chopped pistachios and slice and serve immediately. The pie will keep, refrigerated, for up to 4 days.