Copycat Costco Sheet Cake
A fluffy, creamy dessert perfect for celebrations, this Copycat Costco Sheet Cake is easy to make and tastes just like the original.
Ingredients
For the cake
- 2 boxes 2 (15.25-oz.) boxes of white cake mix (Pillsbury) Yields a fluffy, pliable cake.
- 1/2 tsp 1/2 tsp. kosher salt Enhances sweetness.
- 8 large 8 large egg whites Provides a tender crumb.
- 1 1/2 cups 1 1/2 cups sour cream Enhances moisture.
- 1 cup 1 cup whole milk Adds creaminess.
- 2/3 cup 2/3 cup vegetable oil Ensures a moist finish.
- 2 tsp 2 tsp. pure vanilla extract (preferably clear) Uplifts flavor.
For the mousse
- 1 pkg. 1 (8-oz.) pkg. cream cheese, room temperature Foundation for the mousse.
- 1/2 cup 1/2 cup confectioners’ sugar Adds sweetness.
- 1/2 tsp 1/2 tsp. kosher salt Balances sweetness.
- 1 cup 1 cup whole milk For creamy consistency.
- 1 pkg. 1 (3.4-oz.) pkg. vanilla instant pudding Thickens the mousse.
- 1 cup 1 cup heavy cream For rich texture.
For the frosting
- 2 cups 2 cups vegetable shortening (such as Crisco) For a smooth frosting.
- 1/2 cup 1/2 cup water Keeps frosting blended.
- 1 Tbsp. 1 Tbsp. pure vanilla extract (preferably clear) Adds richness.
- 3/4 tsp 3/4 tsp. kosher salt Enhances flavor.
- 8 cups 8 cups confectioners’ sugar, divided Adds sweetness.
- to taste Sprinkles, for decorating (optional) For a festive finish.
Instructions
Preparation
- Preheat your oven to 350°F (175°C).
- Grease and line two 13x9 metal baking pans with parchment paper.
- In a large bowl, whisk the cake mix and salt together.
- Add in the egg whites, sour cream, milk, vegetable oil, and pure vanilla extract. Beat until combined.
- Divide the batter evenly between the prepared pans.
Baking
- Bake for 20-25 minutes or until a toothpick inserted in the center comes out clean.
- Allow the cakes to cool completely before trimming the tops for even layers.
Making the Mousse
- In a separate bowl, beat together the cream cheese, confectioners’ sugar, and salt until smooth.
- Gradually add in the milk and vanilla pudding mix, mixing until fully incorporated.
- Add the heavy cream and whip until thickened.
Making the Frosting
- Beat together the vegetable shortening, water, vanilla, and salt until smooth.
- Gradually add the confectioners’ sugar, mixing until fluffy.
Assembly
- Start with one layer of cake on a serving platter, add a layer of mousse on top, and place the second layer of cake on top.
- Frost the top and sides of the cake with the creamy frosting.
- Decorate with sprinkles if desired.
Notes
For best results, ensure ingredients like the cream cheese and eggs are at room temperature. Don't rush the frosting for a smooth finish.