For the Banana Cupcakes:
2¾ cups all-purpose flour
1¼ teaspoons baking powder
1 teaspoon baking soda
½ teaspoon salt
½ cup (4 ounces) unsalted butter, at room temperature
¼ cup vegetable shortening, at room temperature
1¾ cups granulated sugar
2 teaspoons vanilla extract
1½ cups mashed very ripe bananas (about 4 bananas)
½ cup buttermilk
For the Vanilla Pastry Cream:
3 cups half-and-half
6 large egg yolks
½ cup granulated sugar
3 tablespoons cornstarch
¼ teaspoon salt
1 teaspoon vanilla extract
To Make the Banana Cupcakes:
Preheat the oven to 325 degrees F. Line two 12-cup cupcake pans with paper liners.
Whisk together the flour, baking powder, baking soda, and salt together into a large bowl and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and shortening together on medium speed until creamy, 3 to 4 minutes. Add the sugar and vanilla and beat on medium speed until fluffy, about 3 minutes. Scrape down the bowl, add the eggs, and beat until just combined. Scrape down the bowl again and add the bananas. Beat until just combined. Turn the mixer to low. Add the flour mixture, alternating with the buttermilk, in three additions, beginning and ending with the flour mixture. Scrape down the bowl, then mix on low speed for a few more seconds.
Fill the cupcake liners about three-quarters full. Bake for 20 to 25 minutes, rotating the pans halfway through the baking time, until a toothpick inserted in the center of a cupcake comes out clean. Transfer the pans to a wire rack and let cool for 20 minutes. Remove the cupcakes from the pans and place them on the rack to cool completely.
To Make the Vanilla Pastry Cream:
Set a fine-mesh sieve over a medium bowl.
In a medium saucepan, bring the half-and-half to a simmer and keep warm.
In a medium bowl, whisk the egg yolks, sugar, cornstarch, and salt together until the mixture is pale, about 1 minute. Whisk half of the warm half-and-half into the egg yolk mixture, then pour that mixture into the remaining half-and-half in the saucepan and cook over medium heat, whisking constantly, until thickened, about 6 minutes. Remove from the heat and whisk in the vanilla. Strain the pastry cream through the sieve and press a piece of plastic wrap directly onto the surface of the cream to prevent a skin from forming. Put in the refrigerator for about 1 hour, or until chilled.
To Assemble the Cupcakes:
If you have a pastry bag, fit the bag with a large tip, fill the bag with the pastry cream, and pipe out enough pastry cream to cover each cupcake.
If you do not have a pastry bag, use an ice cream scoop with a release mechanism to scoop the pastry cream and dispense it onto the top of the cupcake.
You can also use an offset spatula to frost the cupcakes. Top with a single slice of fresh banana or a dried banana chip.
To Serve: You can either top these with the pastry cream and refrigerate until ready to serve; or keep the cupcakes at room temperature and top with the pastry cream right before serving.