Name: Copycat Costco Sheet Cake
Prep time: 25 min
Cook time: 35 min
Total time: 1 h
Cuisine: American
Ingredients: 3 cups all-purpose flour; 2 ½ cups granulated sugar; 1 cup unsalted butter, softened; 1 cup whole milk; 1 cup sour cream; 4 large eggs; 2 ½ tsp baking powder; ½ tsp baking soda; 1 tsp salt; 1 tbsp vanilla extract; 1 tsp almond extract; For Frosting:; 1 ½ cups unsalted butter, softened; 5 cups powdered sugar; 2–3 tbsp heavy cream; 1 tbsp vanilla extract; Pinch of salt

This Copycat Costco Sheet Cake brings the iconic flavor and texture of the beloved Costco classic right into your kitchen. Moist, fluffy cake layers paired with rich, creamy frosting make it perfect for birthdays, celebrations, or any occasion that calls for a crowd-pleasing dessert. With simple ingredients and step-by-step instructions, you can recreate this bakery favorite at home.

Why You’ll Love This Recipe

Costco’s sheet cake is famous for good reason—it’s incredibly moist, generously frosted, and feeds a large group with ease. This homemade version captures all those qualities with a tender vanilla cake base and luscious buttercream frosting. It’s easy to prepare, customizable with your favorite fillings or toppings, and much more economical than buying a full cake from the store.

Ingredients

(Tip: You can find the complete list of ingredients and their measurements in the recipe card below.)

Cake:

All-purpose flour
Granulated sugar
Baking powder
Salt
Unsalted butter
Eggs
Whole milk
Vanilla extract
Sour cream (for added moisture)

Buttercream Frosting:

Unsalted butter
Powdered sugar
Heavy cream or milk
Vanilla extract
A pinch of salt

Optional Filling (to mimic the layered version of the Costco cake):

Vanilla pudding or pastry cream
Whipped cream

Directions

Preheat the oven to 325°F (163°C). Grease and line a large sheet cake pan (typically 12×18 inches) with parchment paper.
Prepare the cake batter by creaming butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition.
Mix in vanilla extract and sour cream, followed by alternating additions of flour mixture and milk until smooth.
Pour the batter into the prepared pan and smooth the top. Bake for 35–40 minutes or until a toothpick inserted in the center comes out clean.
Let the cake cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Prepare the frosting by beating butter until creamy, then gradually adding powdered sugar, cream, and vanilla until light and fluffy.
Optional filling: If layering the cake, slice it horizontally and spread a thin layer of vanilla pudding or whipped cream before frosting.
Frost the cake evenly on all sides and decorate as desired.

Servings and timing

This sheet cake yields approximately 48 servings, making it ideal for large gatherings.
Prep time: 20 minutes
Cook time: 35–40 minutes
Cooling and decorating time: 1–2 hours

Variations

Chocolate version: Replace part of the flour with cocoa powder and use chocolate frosting.
Lemon twist: Add lemon zest and a touch of lemon juice to the batter and frosting.
Almond flavor: Swap vanilla extract for almond extract for a nutty flavor profile.
Layered option: Split the cake horizontally and add a filling like strawberry jam, chocolate ganache, or mousse.
Decorative theme: Use colored frosting or sprinkles to match a party theme.

Storage/reheating

Store the frosted sheet cake in an airtight container or cover with plastic wrap. It can be kept at room temperature for up to 2 days or refrigerated for up to 5 days.
For longer storage, wrap slices individually and freeze for up to 2 months. Thaw at room temperature before serving.
This cake does not require reheating, but chilled cake can be brought to room temperature for the best texture and flavor.

FAQs

How does this cake compare to the original Costco sheet cake?

This recipe closely mimics the flavor, texture, and presentation of the original. While some differences may exist due to commercial baking methods, the moist crumb and rich frosting will feel familiar to Costco fans.

Can I make this cake ahead of time?

Yes, you can bake the cake a day or two in advance and store it wrapped in plastic at room temperature. Frosting can also be made ahead and refrigerated; bring it to room temperature before using.

What size pan do I need?

A standard half-sheet cake pan measuring 12×18 inches is ideal for this recipe. If using smaller pans, divide the batter accordingly and adjust baking time.

Can I use store-bought frosting?

While homemade buttercream provides the best flavor and texture, you can use store-bought frosting for convenience.

How do I layer the cake like Costco’s filled version?

Once cooled, slice the cake horizontally and spread your desired filling—such as vanilla pudding or whipped cream—between the layers before frosting.

Is sour cream necessary?

Sour cream helps add moisture and richness to the cake, closely replicating the texture of the Costco version. If unavailable, you can substitute with plain Greek yogurt.

How long does the cake stay fresh?

When stored properly, the cake remains fresh for up to 5 days in the refrigerator. It can also be frozen for extended storage.

Can I make a smaller version?

Yes, you can halve the recipe and use a 9×13-inch pan. Adjust baking time accordingly and check for doneness with a toothpick.

Is this cake suitable for decorations?

Absolutely. The sturdy yet soft crumb and smooth buttercream make it a great canvas for piping, writing, or themed decorations.

Can I make this recipe gluten-free?

Yes, by using a gluten-free all-purpose flour blend and ensuring all other ingredients are gluten-free, you can make a gluten-free version.

Conclusion

This Copycat Costco Sheet Cake delivers everything you love about the original: a tender, buttery crumb, luscious frosting, and crowd-sized portions. Whether you’re celebrating a birthday, graduation, or just want to indulge in a nostalgic treat, this homemade version will not disappoint. Enjoy the bakery-quality flavor and the satisfaction of making it yourself.