For the cupcakes: Preheat the oven to 350 degrees F. Line a muffin pan with 24 cupcake liners.
In a very large bowl, stir together the flour, sugar, baking powder, baking soda and salt. Add the milk, shortening, Champagne and vanilla. Beat on low to medium speed for about 30 seconds, or until just combined. Scraping the bowl constantly, beat on medium speed for 2 minutes. Add the egg whites and beat for 2 minutes.
Fill the cupcake liners half full with batter and bake until the center springs back when touched, about 12 minutes. Cool before frosting.
For the buttercream: Put the egg whites in the large mixing bowl of a stand mixer fitted with the whisk attachment. Put 1 1/2 cups sugar and 1/2 cup water in a heavy saucepan and bring to a boil over medium to high heat. Bring to a soft ball stage (240 degrees F), 4 to 7 minutes.
Meanwhile, whip the egg whites at high speed until soft peaks form. With the motor running, gradually add the remaining 1/2 cup sugar, continuing to whip until medium peaks form.
When the sugar water reaches 240 degrees F, raise the speed to high and gradually add in the sugar water to the egg whites in a thin stream to avoid cooking the egg whites. Leave the mixer on high for 2 minutes, and then reduce the speed to medium until the mixture has cooled to room temperature, 5 to 8 minutes.
Once cooled, add the butter in increments, scraping the sides of the bowl with a rubber spatula. Add in the vanilla and whip.
Pipe the buttercream on top of the cooled cupcakes.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.