Copycat Costco Sheet Cake Recipe

There are plenty of cake options out there, and we can definitely agree that an elaborately decorated layer cake featuring multiple exquisite flavors is totally delicious. But there's just something even better about a classic white cake with white frosting from the grocery store. And that's exactly what made Costco's sheet cakes so popular.

In June 2020, Costco announced that it wasn't planning to restock half-sheet cakes in its stores, and devoted customers began to rally around a petition to bring them back. Speculation surrounding the announcement attributed the change to the coronavirus pandemic, as customers weren't needing as large of a cake for celebrations such as birthdays, graduations, and anniversaries. After all, a half-sheet cake typically serves 50 people. 

Luckily, we have a fix for those missing the classic sheet cakes from Costco with this Costco copycat cake recipe. By making a quarter sheet-sized cake, you can serve up a rectangular cake for any celebration but on a smaller scale. And the best part? This cake is made entirely from scratch, allowing you to try your hand at learning a new baking skill if you're hoping for a cake fix in a pinch.

To determine how to best make a copycat version of the classic Costco sheet cake, we took a look at the ingredients label. However, the label doesn't share much information when it comes to measurements and method. But, the one thing we know for sure is that a Costco copycat cake recipe needs to be layered, with two layers of vanilla cake, paired with that unrivaled mousse filling, all frosted in a deliciously smooth buttercream.

To make your copycat Costco cake recipe, start by gathering all of your ingredients. You'll need white sugar, flour, baking powder, baking soda, salt, milk, eggs, vegetable oil, and vanilla extract for the cake. For the mousse filling, you'll need heavy whipping cream, milk, and vanilla instant pudding mix. For the buttercream frosting, you'll need butter, milk, powdered sugar, and vanilla extract.

If you wanted to take a shortcut with this recipe, you could opt to swap out the from-scratch vanilla cake recipe and use a boxed mix instead. Prep the box mix according to the instructions on the package before layering and frosting your cake. The same option goes for the frosting if you'd prefer to use a store-bought container of frosting.

The beauty of this simple Costco copycat cake recipe is that it doesn't require very many ingredients or many steps. With a stand mixer, you can whip up this cake from scratch in no time. If you don't have a stand mixer, feel free to utilize a hand mixer with a large bowl instead. Or, a large mixing bowl and a whisk can work for this recipe in a pinch as well. 

Start off by making the batter for your cake. To whip up this simple vanilla cake batter, start by adding the white sugar, flour, baking soda, baking powder, and salt to the bowl of your stand mixer. Using the paddle attachment on the mixer, allow the ingredients to mix well on low speed until combined. Be sure all of your dry ingredients are fully incorporated before moving on to adding in the wet ingredients. 

Once your dry ingredients are mixed, it's time to add in the wet ingredients for your Costco copycat cake.

With your mixer running on medium speed, add in the eggs one at a time. Once the eggs are added, pour in the milk with the mixer running on medium speed. Then, add in the vanilla extract and oil. Continue mixing until the mixture is just combined. Be sure not to over-mix your cake batter.

Once your batter is ready, it's time to bake your cakes. This recipe makes enough batter to bake two 9" x 13" cakes so that you can layer the cake with the mousse filling. To prepare your 9" x 13" pans, add a piece of parchment paper to the bottom of each pan. Spray your cake pans with cooking spray as well. Opting for both of these methods will ensure your cake doesn't stick to the bottom or sides of your cake pan. Place your cakes in the oven at 350 degrees. Allow your cakes to bake for 20 minutes until the top is a nice light golden brown. An inserted toothpick that comes out clean will ensure your cakes are baked in the middle. Once baked, remove your cakes from the oven and set aside to cool while you prepare your filling and frosting.

One of the quintessential components of a Costco white sheet cake is that dreamy, luscious filling we all know and love. It's a mixture between a mousse and a pudding, and it truly makes for the most perfect complement to a vanilla cake.

To make the filling for this Costco copycat cake, you'll want to utilize your stand mixer fitted with the whisk attachment. A hand mixer can work here as well.

Add two cups of heavy whipping cream and half a cup milk to the mixer. Begin whipping your cream on low speed, and then add in the powdered pudding mix. Whip the mixture until the ingredients are well combined, and then increase the speed to whip the mixture into a thick mousse. Once your mixture is ready, allow it to sit in the fridge while your cakes finish cooling and you make the buttercream frosting.

Costco's white cake recipe utilizes a simple buttercream frosting to finish off the cake. But the key here is to make a light and fluffy frosting with the perfect touch of sweetness.

To make the frosting for your Costco copycat cake, start by adding softened butter to the bowl of your mixer. Turn the mixer on with the paddle attachment and whip the butter. Gradually add in two cups of powdered sugar while the mixer is running. Then, gradually add in the milk and the vanilla extract. Continue to slowly add in the rest of the powdered sugar while the mixer is running. Turn off the mixer to scrape down the sides of the bowl with a spatula as needed. Once all ingredients are incorporated and your frosting begins to form, increase the speed of the mixer to whip the frosting. Allowing your frosting to whip (or gallop) on medium speed will add air to the mixture, making it nice and fluffy.

Once your Costco copycat cakes are cooled and your mousse filling is ready, it's time to assemble your layered cake. The easiest way to assemble and decorate your cake is by doing the assembly on a cardboard cake board. These can be found at most major craft stores, and some grocery store bakeries will sell them to customers. If you don't have a cake board, utilizing a platter or a wooden cutting board will do the trick. You could also choose to assemble and frost your cake in one of your 9" x 13" cake pans as well. 

Place one of the cake layers down on the cake board. Use a flat spatula to spread all of the filling on the cake layer. Be sure to spread the filling pretty well until the very edge of the cake.

Place the second cake layer on top of the filling. Press down slightly to be sure the cake is well-assembled before moving onto the frosting.  

Once your Costco copycat cake is assembled and your frosting is made, it's time to frost and decorate your cake. You can choose to utilize a spatula to spread the frosting on your cake, or if you have plastic cake-piping bags along with a large cake icer decorating tip, it will make this process so much easier. 

Frost the cake using your piping bag fitted with the icer tip, or spread the frosting over the sides and top of the cake with your spatula. Be sure to cover the entire cake with frosting. Running the flat-edged spatula over any uneven spots will help to smooth the frosting for that finished celebration-cake look.

If you have access to additional piping bags and decorating tips, consider adding a simple piped border to your cake on the top and bottom and write a message on the top. Add your choice of sprinkles to the cake, or even considering adding a chocolate drizzle.  

Once your cake is assembled, frosted, and decorated, it's time to dig in! This is the moment you've been waiting for, right? Whether you're making this cake for a small celebration or you just feel like eating cake for breakfast and dinner for a few days, this is the perfect answer.

You'll want to be sure you use a nice, sharp knife to cut your cake. If you're divvying it up for a group, make vertical slices down your cake. Then, cut your cake horizontally to make your square slices. Because of the texture of the filling of your cake, it's best to slice your cake with your sharp knife and then rinse or wipe off the knife in between slices for a smooth cut.

Add your slice of cake to a plate, and top it with a scoop of ice cream if desired. Cover any leftover cake with plastic wrap, and keep it in the fridge.