Add the champagne to a medium saucepan and heat over medium high until boiling. Watch closely, and as soon as it starts boiling, turn to a simmer and continue cooking for about 5-8 minutes until the chapagne has reduced by over half.
Once you have about 1/4 cup of the reduced champagne, let cool completely before moving to the enxt step (or else it will melt your frositng).
Once the champagne has cooled, add the softened butter to the bowl of a standing mixer or hand held mixer and mix 2-3 minutes in light and fluffy.
Add powdered sugar and mix on low until it starts to look crumbly. Add in vanilla, champagne, and salt. Mix until combined.
Cover and set aside until ready to frost cake. This can be made 1-2 days in advance and stored in an airtight container in the fridge. Let come to room temperature and remix before using.
When crumbly, turn up speed to medium/medium high and mix 3-5 minutes until light and fluffy. Add in champagne, vanilla, salt, and food coloring and mix until combined.
Cover until ready to frost the cake.
Cake
Preheat oven to 350 ℉.
Line the bottoms of three 6 inch round cake pans with parchment paper and spray with baking spray or cover in butter and flour. Set aside.
Whisk flour, salt, and baking powder in a medium bowl and set aside.
In a bowl, cream softened butter and sugar on medium speed for 2-3 minutes until light and fluffy.
Mix in vanilla and egg whites one at a time, or slowly add boxed egg whites while mixing on low speed. Scrape down the sides of the bowl as necessary to ensure everything is fully mixed.
Alternate adding the dry flour mixture and the champagne, starting and ending with the flour (three additions of flour and two of champagne). Do not over-mix, you want to stop as soon as all the flour is incorporated.
If adding pink food coloring, start adding after the second addition of flour. That way you can add more if needed without overmixing the batter.
Divide the batter evenly between the 3 prepared cake pans and smooth with an offset or regular spatula.
Bake 25-30 minutes, or until you can poke the middle of the cakes with a toothpick and it comes out mostly clean with only a few crumbs on it.
Let cool in the pan for 10 minutes and then let cool completely on a wire rack before frosting.
Frost the layer cake and add any decorations. Enjoy!
Notes
Measure your flour correctly by weighing or using the spoon and swipe method of spooning the flour into the measure cups and swiping the excess off the top with a knife. If you dip the measuring cup directly into the flour, it packs down and you will add too much flour to your recipe.
Make sure all the ingredients are at room temperature, including butter, eggs and champagne.
Use gel food coloring for more vibrant colors that won’t effect the texture of the cake and frosting.
Make sure the cake has cooled completely before frosting, or else it can melt the frosting.