Then, combine the butter and sugar in a mixing bowl of a stand mixer. Beat the ingredients together on high speed for about two minutes, occasionally scraping the sides of the bowl down into the mixture.
Next, in a separate mixing bowl, beat the egg whites for about 1 minute or until fluffy.
Add the vanilla, and beat the mixture on medium speed for one more minute.
Then, combine the flour, baking soda, and baking powder in another medium-sized bowl.
Add the egg mixture and about ⅓ of the dry ingredient mixture to the butter mixture, and beat on medium speed until everything is mixed.
Next, add half of the milk and beat again on medium speed.
Continue alternating between adding the milk and dry ingredients, ⅓ at a time, while beating until all the ingredients are completely mixed. Make sure to scrape down the sides of the bowl into the batter.
Next, grease 3 cake pans with butter, or preferably vegetable shortening. Then, evenly divide and spread the batter between the greased cake pans.If colored layers are desired, you can evenly divide the batter into 3 bowls and mix a small amount of red food coloring into one bowl, and blue food coloring into another. Don't add color to the 3rd, this way you end up with red, white, and blue layers.Use a digital scale to measure out exact and even batter portions.
Bake the cake layers for 30-33 minutes, or until a toothpick in the center of the cake comes out cleanly.
After baking, let the cakes cool for 4 minutes. Then, transfer them to cooling racks and let each one cool completely, until cool to the touch.
After cooling, if your cakes are dome-shaped, carefully cut off the excess, bubbled up part of the cake to make each cake layer totally flat.
Finally, wrap each layer in saran wrap, then again in foil, and freeze until solid.
Frosting
To make the buttercream frosting, first beat the room temp butter by itself in the stand mixer at a high speed until creamy, around 5 minutes, occasionally scraping down the sides of the bowl.
Then, gradually add the sugar and milk alternatively, while continuing to beat at a low speed.
Add in the vanilla extract and beat for 8-10 minutes on high speed, scraping the sides of the bowl into the mixture.
Next, divide the frosting evenly into 4 bowls.
Use a toothpick to add a tiny amount of blue food coloring to one of the bowls and mix until you have a pale blue color, almost like a baby blue. In another frosting bowl, add a few drops of the blue coloring and mix until you have a deeper, more vibrant blue.
Then, add a couple of drops of the red coloring into the 3rd bowl of frosting and mix until you have a vibrant red color. Leave the 4th bowl of frosting plain white.
Next, prepare 3 or 4 piping bags. Scoop the pale blue frosting into one of the piping bags by itself and tie it off.
Then, alternate between scooping the vibrant blue and ¼ of the white frosting into another piping bag prepared with a piping tip for creating swirls. Tie off the bag.
In another piping bag prepared with a tip, alternate between adding the red frosting and ¼ of the white frosting. Tie off the bag.
The remaining white frosting can be transferred to a piping bag for easy distribution, or left in the bowl to scoop out as needed.
Assembling a 3 Layer Cake
First, place a dollop of white buttercream on the center of a revolving cake stand to help keep the cake from sliding. Set a frozen cake layer onto the cake stand, and spread about 1 ½ cups of white icing evenly on top of the cake layer.
Then, add another frozen cake layer and spread another 1 ½ cups of white icing on top.
Top off the cake with the final frozen cake layer and top with white frosting.
After the layers are assembled, move the cake to the refrigerator to chill for 30 minutes.
Next, coat the sides of the assembled cake with a thin layer of white buttercream frosting and spread evenly. This will create a cake coat for the final frosting on the cake.
Place the cake back into the fridge for another 30 minutes.
Then, pipe the pale blue frosting on the prepared cake and spread a thick, even layer over the entire cake. Use a cake scraper to make sure the frosting is evenly spread and smooth.
Finally, using the piping bags of colored buttercream frosting, pipe red, white, and blue rosettes on top of the cake and, if desired, stick patriotic sprinkles into the sides of the cake.
Notes
When baking the cake layers, I like to use Wilton Bake-Easy Strips, so that all my layers come out evenly and to prevent the edges from becoming too crisp. To do this, just soak the bands in water and squeeze out as much as possible before baking. The edges will rise a little bit more when using these bands, so be careful to not let your cake become too thin in the center. Without these strips, the middle of your cake will rise too high, and you’ll have to cut the higher part.
Use Cake Liners with Tabs to easily pick up your cakes after baking, but be sure to grease them so you can easily remove the cakes from the paper.
After baking the layers, I like to freeze the individual layers before putting them together and decorating them. To freeze a layer, take a freshly baked layer out of the oven and let it cool enough to pull out the pan, then wrap it in cellophane and foil and place it onto a baking sheet in the freezer. This allows the cake to hold in all of its moisture and makes stacking and frosting the layers much easier. When decorating, seal all the edges of the cakes with buttercream frosting so none of the moisture escapes the cake, so you don't have to make and use cake moistener. I recommend decorating a frozen cake the day before serving, so it has time to defreeze.
Don’t use too much frosting for your cake, as it will quickly become too sweet and will become hard to manage. When decorating a cake, I recommend a revolving cake stand to make the icing job easier. I use a metal one, but any other revolving cake stand works just fine. When frosting the sides of the cake, I use a bash & chop cutter to evenly distribute the icing.
Icing is butter-based- must be a warm room or will get stiff.
You could also save time by purchasing pre-made frosting if you need to shave off a couple of minutes of the prep time. Additionally, if you don’t have the equipment or time to prepare the batter for a cake, you can purchase any kind of dry cake batter at the store. Doing this will allow you to fully make the cake in about two hours, as you don’t need to go through the process of mixing all of the ingredients.