For the pastry cream:
2 cups half-and-half
½ cup sugar, divided
Pinch of salt
5 large egg yolks
3 tbsp. cornstarch
4 tbsp. cold unsalted butter, cut into 4 pieces
1 1/2 tsp. vanilla extract
For the cupcakes:
3 cups cake flour
1 tbsp. baking powder
½ tsp. salt
1 vanilla bean, split lengthwise
16 tbsp. (1 cup) unsalted butter, at room temperature
2 cups sugar
5 large eggs, at room temperature
1¼ cups buttermilk, at room temperature
1 tbsp. vanilla extract
For the whipped cream:
1¾ cup heavy cream
6 tbsp. confectioners’ sugar
2 tsp. vanilla extract
60 banana slices (about 3 bananas), plus more for topping if desired
1 batch pie dough
1 large egg beaten with 1 tbsp. water
To make the pastry cream, heat the half-and-half, 6 tablespoons of the sugar, and the salt in a saucepan over medium-high heat until simmering, stirring occasionally to dissolve the sugar. Meanwhile, combine the egg yolks and remaining 2 tablespoons sugar in a medium bowl 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 30 seconds. When the half-and-half mixture has reached a simmer, slowly add it to the egg yolk mixture to temper, whisking constantly. Return the mixture to the saucepan, scraping the bowl with a rubber spatula. Return the mixture 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. Press plastic wrap directly on the surface to prevent a skin from forming and refrigerate until cold and set, at least 3 hours and up to 2 days.
To make the cupcakes, preheat the oven to 350° F. Line cupcake pans with paper liners. Set aside. In a medium bowl, combine the cake flour, baking powder and salt. Whisk together and set aside. Add the butter to the bowl of an electric mixer fitted with the paddle attachment. Scrape the vanilla bean seeds into the bowl of the mixer with the butter and discard the pod (or reserve for another use.) Beat on medium-high speed for 3 minutes, until light and creamy in color. Scrape down the sides of the bowl and beat for one more minute.
Add the sugar to the butter mixture, ¼ cup at a time, beating 1 minute after each addition. Mix in the eggs one at a time until incorporated. Scrape down the sides of the bowl after each addition. Combine the buttermilk and the vanilla extract in a liquid measuring cup. With the mixer on low speed, add the dry ingredients alternately with the wet ingredients, beginning and ending with the dry ingredients and mixing just until incorporated. Scrape down the sides of the bowl and mix for 15 seconds longer.
Divide the batter between the prepared paper liners, filling each about 2/3 of the way full. Bake 18-22 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool in the pans 5-10 minutes, then transfer to a cooling rack to cool completely. Replace paper liners and bake remaining batter as before.
To fill the cupcakes, use the cone method to hollow out the center of the cupcakes (I prefer the paring knife method for these cupcakes). Discard the cones. Place a single slice of banana inside of each cupcake. Top with a small spoonful of the pastry cream and another slice of banana on top of that.
To frost the cupcakes, combine the cream and confectioners’ sugar in the bowl of an electric mixer fitted with the whisk attachment. Whip on medium-high speed until stiff peaks form, being careful not to over-beat. Blend in the vanilla extract. Transfer the whipped cream to a pastry bag fitted with a decorative tip (I used a large unlabeled star tip). Pipe a swirl of whipped cream on top of each cupcake.
To finish, preheat the oven to 400˚ F. Line a baking sheet with a silicone baking mat or parchment paper. Roll out the pie dough on a lightly floured surface and cut out small decorative rounds with a cookie cutter. Transfer the rounds to the prepared baking sheet and brush lightly with the egg wash. Bake about 15 minutes, or until light golden brown. Let cool completely. (The pie dough rounds can certainly be made in advance and stored in an airtight container.) Just before serving, top cupcakes with a round of pie crust and an additional banana slice, if desired.