Copycat Costco Sheet Cake (Print)

Fluffy cake layers with velvety mousse and bakery-style frosting, perfect for celebrations and gatherings.

# Ingredients:

→ Cake

01 - 2 boxes (432 g each) white cake mix
02 - 0.5 teaspoon kosher salt
03 - 8 large egg whites
04 - 360 ml sour cream
05 - 240 ml whole milk
06 - 160 ml vegetable oil
07 - 2 teaspoons clear pure vanilla extract

→ Vanilla Cheesecake Mousse

08 - 227 g cream cheese, room temperature
09 - 60 g confectioners' sugar
10 - 0.5 teaspoon kosher salt
11 - 240 ml whole milk
12 - 96 g package vanilla instant pudding mix (dry)
13 - 240 ml heavy cream

→ Bakery-Style Frosting & Assembly

14 - 460 g vegetable shortening
15 - 120 ml water
16 - 1 tablespoon clear vanilla extract
17 - 0.75 teaspoon kosher salt
18 - 960 g confectioners' sugar, divided
19 - Sprinkles (optional)

# Steps:

01 - Preheat oven to 175°C. Grease two 33×23 cm metal baking pans, line with parchment, and lightly coat with cooking spray.
02 - In a stand mixer bowl, combine white cake mix and salt; mix briefly. Add egg whites, sour cream, milk, vegetable oil, and vanilla extract. Beat on medium speed for about 2 minutes until smooth.
03 - Evenly divide batter between prepared pans. Bake in preheated oven for 20–25 minutes until tops are lightly browned and spring back when touched.
04 - Allow cakes to cool in pans for 10 minutes. Invert onto wire racks, remove parchment, and cool completely. Level any domed tops with a serrated knife.
05 - In a clean mixing bowl, beat cream cheese, confectioners' sugar, and salt on medium speed until smooth, about 1–2 minutes. Add milk and dry pudding mix; mix for 1 minute. Pour in heavy cream and beat until thick and light, approximately 1–2 minutes.
06 - Place one cake layer on a platter. Spread mousse evenly over the surface, leaving a 1.25 cm border around the edge. Position the second cake layer on top, trimmed side facing down. Cover and chill to set.
07 - In a stand mixer, beat vegetable shortening, water, vanilla extract, and salt until creamy and smooth. Gradually add confectioners' sugar in 120 g increments, mixing on low after each addition. Increase to medium-high and whip for 1 minute until fluffy.
08 - Apply an even layer of frosting over cake using an offset spatula. Fill a piping bag fitted with a star tip, pipe decorative shell borders along edges, and finish with sprinkles if desired.

# Additional Notes:

01 - Ensure cake layers are fully cooled before frosting to prevent melting. For clean slices, chill the assembled cake for 30 minutes before serving.

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