Instructions

Make the cupcakes:

1. For the cupcakes: Preheat the oven to 350F degrees. Line a 12-cup cupcake/muffin pan with cupcake liners. Set aside.
2. Melt the butter and chocolate together in the microwave. Microwave in 30 second increments, stirring between each time. You may also melt the butter and chocolate over low heat on the stovetop. Stir until smooth and set aside to slightly cool.
3. In a medium sized bowl, toss the cocoa powder, flour, baking soda, baking powder, and salt together until thoroughly combined. Set aside. In a large bowl, whisk the eggs, sugar, brown sugar, and vanilla together until smooth. Add the cooled butter/chocolate and whisk until smooth. Add half of the flour mixture, then half of the buttermilk. Repeat until everything is added. Stir until *just* combined; do not overmix. The batter will be very thick like pudding.
4. Divide the batter between 12 liners in your cupcake pan. Bake for 18 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before frosting.

Make the custard:

1. Bring the milk and sliced bananas to a boil in a large saucepan. If you’re using vanilla extract, just leave it out for now. Turn off the heat, and allow the mixture to steep until cool. You can also do what I did, and store it in the refrigerator overnight for extra banana flavor.
2. When you’re ready to continue, bring the milk back to a simmer. Strain the mixture through a fine mesh sieve, pressing lightly to ensure you’re getting out as much liquid as possible, but not so much that you’re pressing the banana solids through the sieve. Check to make sure you have 2 cups of milk; if not, add a little milk until you’re back up to 2 cups.
3. In a mixing bowl, whisk together the egg and yolks together with the reserved vanilla caviar or vanilla extract (if using extract instead of whole vanilla bean), sugar, cornstarch, and salt. Slowly drizzle in the hot milk, whisking constantly, until you’ve incorporated at least half of it. Then add the tempered egg mixture back into the hot milk on the stove, whisking constantly. Continue whisking the egg mixture over medium heat until it’s very thick and begins to bubble. Once it begins to bubble, continue to cook for another minute.
4. Pour the mixture into the bowl of a stand mixer fitted with the paddle attachment and beat at low speed until the cream has cooled enough so that the mixing bowl is neutral to the touch. Add the peanut butter, and continue to beat at medium speed until well combined, scraping the paddle and the sides of the bowl as needed.
5. Scrape the custard into an airtight container (you can press plastic wrap into the top to prevent a skin from forming), and refrigerate until ready to use. I used a resealable bag, which had the added bonus of allowing me to simply snip off a corner of the bag and pipe the custard directly onto the cake when I was ready to do final assembly.

Make the frosting:

1. Place the peanut butter and butter in a large mixing bowl. Blend with an electric mixer on low speed until fluffy, 30 seconds.
2. Stop the machine. Add the confectioners’ sugar, 3 tablespoons milk, and the vanilla. Blend with the mixer on low speed until the sugar is well combined, 1 minute.
3. Increase the speed to medium and beat until the frosting lightens and is fluffy, 1 minute more. Blend in up to 1 tablespoon milk if the frosting seems too stiff.