For the cupcakes:
1/2 cup unsalted butter, softened
1 cup granulated sugar
1 teaspoon vanilla
1 3/4 cups all-purpose flour
1/2 teaspoon baking soda
1/4 teaspoon baking powder
1/4 teaspoon salt
1/2 cup sour cream
1/2 cup champagne (no need to use the good stuff here…my $4 bottle of Andre worked quite nicely)
Preheat the oven to 350 degrees, and line cupcake tins with 17 paper liners. Adjust oven rack to middle position.
Cream together butter and sugar until light and fluffy. Add eggs one at a time, and beat well after each addition. Beat in vanilla. In a medium bowl, whisk together flour, baking soda, baking powder, and salt. Set aside. In a separate bowl, stir together sour cream and champagne.
With the mixer on low speed, add the flour mixture and the champagne mixture to the butter/egg mixture alternately, beginning and ending with the flour mixture.
Using level 1/4 cup measures, divide batter between prepared cupcake tins. Bake for 17-22 minutes, rotating cupcake tins halfway through baking time. Set aside to cool completely before filling and frosting.
For the pastry creme filling:
1/2 cup heavy cream, divided
1/2 cup champagne
2 tablespoons cornstarch
5 tablespoons granulated sugar
1 whole egg
2 egg yolks
2 tablespoons unsalted butter
1 teaspoon vanilla
In a medium sized bowl, whisk together 1/4 cup of the heavy cream and the cornstarch. Set aside.
In a saucepan, combine the remaining 1/4 cup heavy cream, the champagne, and the sugar. Stir to combine, and bring to a boil over medium heat.
While waiting for the mixture to boil, beat the egg, and yolks into the heavy cream and cornstarch mixture.
When the champagne mixture is boiling, remove from the heat, and add 1/3 of it to the egg mixture, whisking constantly so the eggs don’t cook. Return the champagne mixture to a boil, and add in the egg mixture in a slow stream, whisking constantly.
Continue to whisk until the mixture thickens, and remove from heat. Stir in butter and vanilla, and continue to stir until the butter has melted completely.
Allow the mixture to cool for 15 minutes before filling cupcakes. Using a paring knife, cut out the center of the cupcake, and fill with cooled pastry creme. I spooned mine into a large ziploc bag, and snipped off the end to make this easier.
You will have leftover pastry creme. I’m sure you can figure out what to do with it! Allow the filling to cool completely before frosting the cupcakes.
For the frosting:
1 cup plus 1 tablespoon champagne
2 sticks unsalted butter, softened
2 1/2 cups powdered sugar
Add 1 cup of champagne to a small saucepan. Simmer over medium-high heat, until it has reduced to 2 tablespoons (about 7-10 minutes, but keep an eye on it!) Transfer to a small bowl to cool completely.
In a large bowl, beat together butter and powdered sugar on medium speed until fluffy. Add in reduced champagne, and the remaining 1 tablespoon of champagne and beat until smooth.
Store cupcakes in the refrigerator, and bring to room temperature 15 minutes before serving.