Dessert

Copycat Costco Sheet Cake Recipe

ByMariam Harutyunyan June 26, 2026June 26, 2026

Introduction

This Copycat Costco Sheet Cake is a delightful treat that combines a moist, tender white cake with a rich vanilla cheesecake mousse and a creamy bakery-style frosting. Perfect for gatherings or as a special dessert, this layered sheet cake is sure to impress with its luscious flavors and beautiful presentation.

A square vanilla layer cake with two visible soft, light yellow sponge layers is covered in smooth, thick white frosting. The top and edges have a thick ruffled frosting border decorated with bright, colorful round and stick sprinkles in red, blue, yellow, orange, green, pink, and purple. A slice is being lifted with a teal spatula showing the cake’s soft crumb texture. To the right, a stack of plain pink plates rests on a white marbled surface sprinkled with more of the same bright sprinkles. The overall look is clean, fresh, and festive. Photo taken with an iphone --ar 4:5 --v 7

Ingredients

Cooking spray
2 (15.25-oz.) boxes white cake mix (we used Pillsbury)

1/2 tsp. kosher salt
8 large egg whites

1 1/2 cups sour cream
1 cup whole milk

2/3 cup vegetable oil
2 tsp. pure vanilla extract (preferably clear)
1 (8-oz.) package cream cheese, room temperature

1/2 cup (57 g) confectioners’ sugar
1 (3.4-oz.) package vanilla instant pudding
1 cup heavy cream

2 cups vegetable shortening (such as Crisco)
1/2 cup water
1 tbsp. pure vanilla extract (preferably clear)

3/4 tsp. kosher salt
8 cups (904 g) confectioners’ sugar, divided
Sprinkles, for decorating (optional)

A piping bag, a star tip

Instructions

Step 1: Preheat your oven to 350°F (175°C). Lightly grease a large sheet pan with cooking spray. In a large bowl, combine the cake mixes, kosher salt, egg whites, sour cream, milk, vegetable oil, and vanilla extract. Using an electric mixer, beat on medium speed until smooth and fully combined.
Step 2: Pour the batter evenly into the prepared pan and bake for 35–40 minutes or until a toothpick inserted into the center comes out clean. Let the cake cool completely in the pan on a wire rack.

Step 3: To make the vanilla cheesecake mousse, beat the cream cheese and confectioners’ sugar together until smooth. Add the vanilla pudding mix and beat until combined. In a separate bowl, whip the heavy cream until stiff peaks form, then gently fold it into the cream cheese mixture. Spread this mousse evenly over the cooled cake and chill in the refrigerator while preparing the frosting.
Step 4: For the bakery-style frosting, beat the vegetable shortening and 3/4 teaspoon kosher salt in a large bowl until smooth. Slowly add the water and vanilla, then gradually mix in 7 cups of the confectioners’ sugar, beating on medium speed until fluffy. If the frosting is too thick, add a little more water, one teaspoon at a time, until spreadable.
Step 5: Gently spread the frosting over the chilled mousse layer. Using a piping bag with a star tip, decorate the top with additional frosting swirls if desired. Sprinkle with colorful sprinkles for a festive touch.

Step 6: Refrigerate the assembled cake for at least 2 hours before serving to allow the layers to set properly. Slice into squares and enjoy!

Tips & Variations

For extra moist cake, make sure not to overbake; start checking for doneness at 35 minutes.
Use clear vanilla extract to maintain the bright white color of the cake and frosting.

Substitute sour cream with Greek yogurt for a tangier flavor and added protein.
Decorate with fresh berries instead of sprinkles for a fresh twist.
Make sure the cream cheese is at room temperature to avoid lumps in the mousse.

Storage

Store the cake covered in the refrigerator for up to 4 days. To keep the frosting fresh, cover the cake lightly with plastic wrap or place it in an airtight container. When ready to serve, let the cake sit at room temperature for 15–20 minutes for the best texture. Do not freeze, as the mousse and frosting textures may change.

How to Serve

A slice of three-layer cake sits on a white plate placed on a white marbled textured surface. The bottom and middle layers are light, spongy cake with a soft yellow cream filling in between. The top layer is thick white icing, smooth and creamy. The cake's edges are decorated with white icing piped in swirls, sprinkled with colorful, thin, rod-shaped sprinkles in red, pink, blue, green, purple, orange, and yellow. Some sprinkles have fallen onto the plate and surface. In the background, a larger, frosted cake with the same icing and sprinkles is partially visible. Photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I make this cake ahead of time?

Yes, this cake is perfect for making a day ahead. After assembling, refrigerate it overnight to allow the mousse and frosting to set fully. Just add any fresh decorations right before serving.

Can I use a different cake mix flavor?

While white cake mix is recommended to keep the classic Costco cake flavor, you could experiment with yellow cake mix for a richer taste. Avoid using chocolate or heavily flavored mixes as they will alter the texture and overall profile.