Preheat oven to 350 degrees.

Grease and flour two 8 inch cake pans. Set aside.

In a large bowl, whisk together the flour, baking powder and salt. Set aside.

In the bowl of a stand mixer, beat the butter and sugar together until fluffy. Add the egg whites, one at a time, fully incorporating after each addition. Add the egg and vanilla, mix to combine.

Alternate adding the flour mixture and champagne, starting and ending with the flour. Stir in the sour cream until well combined.

Add 1-2 drops of Magenta color gel until the desired color is achieved.

Divide the batter evenly between the two cake pans and smooth the tops with a spatula.

Bake for approximately 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Transfer to a wire rack to cool for 10 minutes, then turn the cakes out onto the rack to cool completely.

To make the buttercream, add the butter to the bowl of a stand mixer and beat until fluffy.

Add vanilla and 1 cup confectioners' sugar beating on medium speed until well combined.

Slowly add 1 cup more confectioners' sugar to the frosting and beat until smooth.

Turn the mixer to low and stir in the champagne.

Begin adding remaining sugar to the frosting one cup at a time at medium speed, beating well until the desired consistency is achieved.

Add 1-2 drops color gel if you'd like pink frosting.

Transfer to an airtight container and store at room temperature for 2 hours or overnight.

To frost the cake, place one cake layer on a cake stand or serving plate.

Top with approximately 2/3 cup of frosting. Spread evenly to coat the top and sides of the cake. Place the remaining cake layer on top and apply a thin coat of frosting all over the cake. Chill for 20mins.

Top the cake with another 2/3 cup frosting. Smooth the top and sides of the cake with the frosting.

Decorate with rosettes and sprinkles, if desired.

Serve immediately or chill overnight.