Copycat Costco Sheet Cake
This indulgent Copycat Costco Sheet Cake features fluffy layers, creamy mousse filling, and rich frosting, perfect for any celebration.
Ingredients
For the Cake
- 2 boxes white cake mix The backbone of the cake, providing a light and airy foundation.
- 8 large egg whites For that perfect rise.
- 1.5 cups sour cream Adds moisture and richness.
- 1 cup whole milk Contributes to the cake's flavor and texture.
- 1/2 cup vegetable oil For added richness.
- 1 tbsp pure vanilla extract For a fragrant touch.
- 1 tsp kosher salt Balances the sweetness.
For the Mousse Filling
- 8 oz cream cheese At room temperature.
- 1 cup confectioners’ sugar For a smooth, sweet layer.
- 1 tbsp instant vanilla pudding mix Thickens the mousse and elevates flavor.
- 1 cup heavy cream Helps create that luxurious experience.
- 1 pinch kosher salt
For the Frosting
- 1 cup vegetable shortening
- 1/4 cup water
- 1 tbsp vanilla extract
- 1 tsp salt
- 8 cups confectioners’ sugar Ensures the frosting is fluffy and sweet.
- to taste sprinkles For decoration.
Instructions
Preparation
- Preheat your oven to 350°F.
- Grease and line two 13x9 metal baking pans with parchment paper.
- In a large bowl, whisk together the cake mix and kosher salt until well combined.
- Add in the egg whites, sour cream, whole milk, vegetable oil, and vanilla extract. Beat until smooth.
- 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 fully in the pans before trimming for even stacking.
Mousse Filling
- Beat together the cream cheese, confectioners’ sugar, and a pinch of kosher salt until smooth.
- Gradually mix in the milk and instant pudding mix, beating until combined.
- Add the heavy cream and whip until thickened to desired consistency.
Frosting & Assembly
- Beat the shortening, water, vanilla extract, and salt together until smooth.
- Gradually add the confectioners’ sugar, mixing on low until fluffy.
- Place one layer of cake on your serving platter. Spread a generous amount of mousse filling on top, then layer the second cake over it.
- Cover the entire cake with frosting and finish with sprinkles.
Notes
For best results, sift flour and sugar for frosting and mousse to eliminate lumps. Personalize your cake by adding flavor extracts like almond or lemon. Refrigerate the mousse briefly before assembly for enhanced flavor.