In my opinion, this is one of, if not the most delicious cupcake I’ve baked. It’s also one of the most labor intensive. The next time I make them I will make the custard the day before to save some time. The frosting can be prepared up to five days in advance and kept refrigerated. Bring the frosting to room temperature and beat for two minutes for frosting consistency. These are definitely worth the effort. They are mouth-watering and look beautiful.
1/2 cup butter, softened
1-1/2 cups sugar
1 cup (8 ounces) sour cream
1 teaspoon vanilla extract
2 cups all-purpose flour
1 teaspoon baking soda
1/4 teaspoon salt
2 medium ripe bananas, mashed (about 1 cup)
Banana Cream Custard Filling:
1 cup milk
1 cup heavy cream
1/4 cup cornstarch
1/2 cup + 2 tablespoons sugar
1 tablespoon vanilla
1/4 teaspoon kosher salt
Swiss Vanilla Buttercream Frosting:
5 large egg whites
1- 1/2 cup sugar
2 cups unsalted butter, diced and softened
1/4 teaspoon salt
1 1/2 teaspoons vanilla extract
1 cup bittersweet chocolate, chopped
1 cup heavy cream
1 tablespoon corn syrup
For the Cupcake:
In a large bowl, cream butter and sugar until light and fluffy. Add the eggs, sour cream and vanilla. Combine the flour, baking soda and salt; gradually add to the creamed mixture. Stir in bananas. Scoop into muffin liners. Bake at 350F for 15-20 minutes until a toothpick inserted in the center comes out clean. Cool in pans for 10 minutes then remove to a wire rack to cool.
For the filling:
Place all ingredients in a food processor bowl or blender and process to combine. Pour mixture into a saucepan over a medium heat and cook until mixture starts to bubble, making sure to constantly whisk. Continue to cook the mixture until it thickens, about 5-7 minutes, or until it coats the back of a spoon. Remove from heat and let it cool slightly.
For the Frosting:
Combine egg whites and sugar in a bowl placed over simmering water. Bring mixture to 150 degrees F while whisking constantly. Transfer mixture to stand mixer bowl, fitted with a whisk attachment and beat on medium speed until mixture cools and doubles in volume. Add butter one piece at a time, mixing to incorporate after each addition. Add salt and vanilla and mix to combine. The frosting may appear to look separated, keep mixing and and it will come together (this commonly happens when making Swiss Meringue Buttercream.)
For the ganache:
To make the ganache, place the chopped chocolate in a heatproof bowl. Bring the cream to a simmer over medium-high heat. Remove from the heat and pour the hot cream over the chocolate; let stand 1-2 minutes. Whisk together until a thick, smooth ganache forms. Blend in the corn syrup. Let stand at room temperature at least 10 minutes so the ganache is not hot.
To stuff the cupcakes: Create a well in the center of the cupcake using either apple corer, the large end of cupcake tip, or hand-carve a well using a paring knife. Fill well with banana cream custard filling.
To frost the cupcakes: Fill a pastry bag fitted with a large round tip and start piping from the outside working in to the center to create one even layer. Freeze cupcakes for 20 minutes before dipping in ganache, so that the buttercream frosting does not melt. Remove cupcakes and dip in ganache, and then rim with sprinkles. Return cupcakes to freezer for five minutes for chocolate to set. Remove from freezer and finish piping frosting on top and garnish with a Maraschino cherry.