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Copycat Costco Sheet Cake

A homemade version of the iconic bakery sheet cake featuring soft vanilla layers, a rich vanilla cheesecake mousse filling, and pristine white buttercream frosting.
Print Recipe
Prep Time 45 minutes
Cook Time 35 minutes
Total Time 1 hour 20 minutes
Servings: 24 slices
Course: Dessert
Cuisine: American
Calories: 485
Ingredients Equipment Method Notes

Ingredients
  

Vanilla Cake Layers
  • 1.5 cups All-purpose flour
  • 1.5 cups Cake flour spooned and leveled
  • 2 cups Granulated sugar
  • 1 tablespoon Baking powder
  • 1 teaspoon Kosher salt
  • 0.5 cup Unsalted butter softened to room temperature
  • 0.5 cup Vegetable oil
  • 4 Large eggs room temperature
  • 1 cup Buttermilk room temperature
  • 0.25 cup Sour cream room temperature
  • 1 tablespoon Pure vanilla extract
Vanilla Mousse Filling
  • 8 oz Cream cheese softened
  • 0.5 cup Powdered sugar
  • 1 box Instant vanilla pudding mix 3.4 oz box, dry mix only
  • 1.5 cups Heavy whipping cream cold
  • 1 teaspoon Pure vanilla extract
White Bakery Buttercream
  • 1 cup Unsalted butter softened
  • 0.5 cup Vegetable shortening
  • 5 cups Powdered sugar sifted
  • 0.25 cup Heavy whipping cream adjust as needed
  • 1 tablespoon Clear vanilla extract
  • 0.25 teaspoon Salt
  • 0.25 cup Rainbow sprinkles for decorating

Equipment

  • Stand Mixer
  • Two 9x13 Baking Pans
  • Piping Bag with Star Tip

Method
 

  1. Preheat oven to 350°F (175°C). Prepare two 9x13 inch baking pans with non-stick spray and parchment paper.
  2. In a stand mixer, whisk together the all-purpose flour, cake flour, granulated sugar, baking powder, and salt.
  3. On low speed, add the softened butter one tablespoon at a time, followed by the vegetable oil, mixing until it resembles coarse sand.
  4. In a separate bowl, whisk the eggs, buttermilk, sour cream, and vanilla. Slowly pour this wet mixture into the dry ingredients while mixing on low.
  5. Turn the mixer to medium speed and beat the batter for exactly 2 minutes to build structure.
  6. Divide batter evenly between the pans. Bake for 22-28 minutes until a toothpick comes out clean. Let cool completely.
  7. To make the filling, beat the softened cream cheese and powdered sugar until smooth. Add the dry pudding mix and vanilla. Slowly stream in the cold heavy cream while mixing, then whip on high until stiff, fluffy peaks form. Refrigerate.
  8. For the frosting, beat the butter and vegetable shortening until fluffy. Gradually add sifted powdered sugar, clear vanilla, salt, and heavy cream. Whip until light and airy.
  9. Assemble the cake by placing one layer on a serving board. Spread the mousse filling evenly over the top, leaving a small border. Place the second cake layer on top.
  10. Crumb coat the cake with a thin layer of frosting and chill for 20 minutes. Frost the entire cake with the remaining buttercream, pipe decorative borders, and apply rainbow sprinkles. Chill before serving.

Notes

Using clear vanilla extract in the frosting is essential to keep it bakery-white. Ensure all cake batter ingredients are at room temperature to avoid a dense texture. Store the finished cake in the refrigerator.