Vanilla Sheet Cake Recipe (Costco Copycat!)

closeup of copycat costco vanilla sheet cake

Vanilla Sheet Cake Recipe (Costco Copycat!)

This Vanilla Sheet Cake Recipe is a delicious dupe of Costco sheet cake. Easy to make, assemble, and decorate — no special order needed!

Author: Donna Elick

Servings: -24

Prep Time45

Cook Time35

Total Time1 20

Ingredients

For the Vanilla Sheet Cake:

5 1/2 cups cake flour
4 cups granulated sugar
2 tablespoons baking powder
1 teaspoon kosher salt
1 1/2 cups 3 sticks unsalted butter, softened
8 large egg whites
2 large whole eggs
2 cups whole milk
2 teaspoons pure vanilla extract

For the Mousse:

1 cup heavy cream cold
8 ounces cream cheese softened
1/2 cup powdered sugar
1/2 cup whole milk
3.4 ounce package instant vanilla pudding mix

For the Buttercream:

2 cups unsalted butter, softened 4 sticks
8 cups powdered sugar
2 teaspoons pure vanilla extract
6 - 7 tablespoons whole milk adjust as needed for consistency

Instructions

For the Sheet Cakes:

Preheat the Oven: Preheat the oven to 350°F. Grease and line two 9x13-inch cake pans with parchment paper.
Mix the Dry Ingredients: In a large bowl, whisk together the cake flour, sugar, baking powder, and salt.
Incorporate the Butter: Add the softened butter and mix on low speed until the mixture forms coarse crumbs.
Add the Eggs: Mix in the egg whites and whole eggs, one at a time, until fully incorporated.
Finish the Batter: Slowly pour in the milk and vanilla extract, mixing on medium speed until smooth.
Bake the Cakes: Divide the batter evenly between the pans. Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.
Cool the Cakes: Allow the cakes to cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

For the Mousse:

Whip the Heavy Cream: In a large bowl, beat the heavy cream on high speed until stiff peaks form. Set aside.
Blend the Cream Cheese & Sugar: In a separate bowl, beat the cream cheese and powdered sugar until smooth.
Add the Pudding: Gradually mix in the milk and pudding mix, beating until thickened and smooth.
Fold in the Whipped Cream: Gently fold the whipped cream into the cream cheese mixture until fully combined. Refrigerate until needed.

For the Buttercream:

Beat the Butter: In a large bowl, beat the softened butter on medium speed until smooth.
Incorporate the Sugar & Vanilla: Gradually add the powdered sugar, then mix in the vanilla extract.
Adjust Consistency: Add milk, one tablespoon at a time, until the frosting reaches a spreadable consistency. Beat on high for 1–2 minutes to make it fluffy.

To Assemble:

Trim the Cakes: Use a serrated knife to trim any domed tops to create even layers.
Add the Mousse Layer: Place one cake layer on a serving tray and spread an even layer of mousse over the surface.
Layer the Cakes: Place the second cake on top, aligning the edges.
Frost the Cake: Spread the buttercream frosting evenly over the top and sides of the cake.
Decorate: Use a piping bag with a star tip to create borders or decorative swirls. Top with rainbow sprinkles, shaved chocolate, or crushed cookies if desired.
Serve: Slice into portions and enjoy!

Notes

Make-Ahead Tips: The sheet cakes and mousse can be made a day in advance. Wrap cakes tightly and refrigerate mousse until assembly.

Storage: Store the assembled cake in an airtight container in the refrigerator for up to 3 days. Allow it to come to room temperature before serving for the best texture and flavor.

Freezing: Wrap cooled cakes tightly in plastic wrap and store in the freezer for up to 3 months. Thaw overnight in the refrigerator before decorating.

Buttercream can also be stored in an airtight container in the freezer for up to 3 months. Bring to room temperature and re-whip before using.

Decorating Tips: If sprinkles aren’t your style, try topping with edible flowers, shaved chocolate, or cookie crumbles.

Leveling the Cake: For a flat, even surface, use a cake leveler or a serrated knife. This helps prevent the mousse from shifting.

Chilling the Mousse: After layering the mousse, chill the first cake layer for 15–20 minutes before adding the second layer. This helps the mousse set and prevents shifting.

Whipping Tips: For best results, chill your mixing bowl and beaters for 10 minutes before whipping the heavy cream to ensure stiff peaks form quickly.

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