Make the Cake Layers

1. Add all of the champagne to a medium sized saucepan and cook over medium heat until you’ve got 1 cup remaining. Don’t boil. To measure how much champagne remains, pour into a glass measuring cup. Add it back to the pan if it needs longer to cook down. When done, refrigerate until cool.
2. Prepare three 8-inch cake pans with parchment paper circles in the bottom and grease the sides. Preheat oven to 350°F (176°C).
3. In a large mixing bowl, cream the butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.
4. Add sour cream and vanilla extract and mix until well combined.
5. Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
6. Combine dry ingredients in a separate bowl, then combine the milk and 3/4 cup of the cooked and cooled champagne to a small measuring cup.
7. Add half of the dry ingredients to the batter and mix until well combined. Add the champagne mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
8. Divide the batter evenly between the cakes pans and bake for about 23-27 minutes, or until a toothpick comes out with a few crumbs.
9. Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.

Make the Strawberry Frosting

1. Puree the strawberries in a food processor. Strain the puree through a fine mesh sieve to remove the seeds.
2. In a large mixer bowl, beat the butter and shortening together until smooth.
3. Slowly add half of the powdered sugar and mix until smooth.
4. Add 3-4 tablespoons of strawberry puree and mix until smooth.
5. Slowly add remaining powdered sugar and mix until smooth. Add additional strawberry puree, as needed to get the right consistency. Set aside.

Make the Champagne Frosting

1. Beat the butter and shortening together until smooth.
2. Slowly add half of the powdered sugar and mix until smooth.
3. Add 3 tablespoons of champagne and mix until smooth.
4. Slowly add remaining powdered sugar and mix until smooth.
5. Add remaining cooked-down champagne (from the cake), as needed. If you run out of champagne and the frosting is still too thick, add a touch of water or milk. You want the frosting to be a little bit sticky, so that the sprinkles stick easily later.

Assemble the Cake

1. Use a large serrated knife to remove the domes from the top of the cakes so that they’re flat. Place the first cake on a serving plate or a cardboard cake round.
2. Set aside about 1/2 cup of strawberry frosting, then spread about half of the remaining strawberry frosting evenly on top of the cake layer.
3. Add the second layer of cake and another cup of strawberry frosting.
4. Top the cake with the remaining layer and frost the cake with the champagne frosting. Refer to my tutorial for frosting a smooth cake, if needed.
5. Press the sprinkles into the sides of the cake. Do this immediately, before the frosting crusts and the sprinkles will no longer stick.
6. Use the strawberry frosting that was set aside before to pipe shells around the edge of the cake. I used Ateco tip 844, but Wilton 1M or 2D would work as well.
7. Sprinkle the top of the cake with some additional sprinkles, if desired.