Make the Peanut Butter Pastry Cream: Heat the half-and-half, 6 tablespoons of the sugar, and the salt in a medium heavy-bottomed saucepan over medium heat until simmering, stirring occasionally to dissolve the sugar.
Meanwhile, whisk the egg yolks in a medium bowl until thoroughly combined. Whisk in the remaining 2 tablespoons sugar and whisk until the sugar has begun to dissolve and the mixture is creamy, about 15 seconds. Whisk in the cornstarch until combined and the mixture is pale yellow and thick, about 20 seconds.
When the half-and-half mixture reaches a full simmer, gradually whisk the simmering half-and-half into the yolk mixture to temper. Return the mixture to the saucepan, scraping the bowl with a rubber spatula; return to a simmer over medium heat, whisking constantly, until a few bubbles burst on the surface and the mixture is thickened and glossy, about 30 seconds. Off the heat, whisk in the butter and vanilla. Strain the pastry cream through a fine-mesh sieve set over a medium bowl, then whisk in the peanut butter until thoroughly combined and smooth. Press plastic wrap directly on the surface to prevent a skin from forming and refrigerate until cold and set, at least 3 hours or up to 2 days.
Make the Pretzel Crust: Preheat the oven to 350 degrees F. In a medium bowl, stir together the crushed pretzels and sugar. Pour the melted butter over top and, using a fork, stir until the mixture is evenly moistened. Press the mixture into a 9-inch pie pan and bake for 10 to 12 minutes, until lightly browned. Place on a wire rack and cool completely.
Make the Chocolate Ganache: Place the chopped chocolate in a medium bowl. Microwave the butter and cream together for 1 minute, or heat in a small saucepan until bubbling. Pour the cream mixture over the chocolate and stir until the chocolate is completely melted and smooth. Whisk in the vanilla and then whisk in powdered sugar until smooth. Pour over the crust while ganache is still warm. Refrigerate for 30 minutes, or until set.
Arrange the sliced bananas over top of the chocolate ganache, then spread the chilled peanut butter pastry cream over top of the bananas. (You may need to whisk the pastry cream to loosen it up a bit.)
Make the Whipped Cream: Pour the heavy cream, sugar and vanilla extract into the bowl of a stand mixer fitted with the whisk attachment. Turn the mixer to medium speed and whip to soft peaks, about 3 to 4 minutes. Spread the whipped cream evenly over the pastry cream.
Garnish with crushed pretzels, chocolate and peanut butter, if desired. Pie leftovers can be covered with plastic wrap and refrigerated for up to 2 days.