Copycat Costco Sheet Cake Recipe

Step 1

Preheat your oven to 350 degrees. In the bowl of a stand mixer fitted with the paddle attachment, mix white sugar, flour, baking powder, baking soda, and salt.

Step 2

Add in the eggs one at a time and continue mixing.

Step 3

With the mixer running, add in two cups milk, four teaspoons vanilla extract, and vegetable oil. Mix until just combined.

Step 4

Generously spray two 9" x 13" cake pans with cooking spray. Add a piece of parchment on the bottom of the pan to be sure your cake won't stick to the pan. Divide the batter between the two cake pans and place in the oven. Bake cakes for 20 minutes until light golden brown. A toothpick inserted into the cake will tell you if the cake is completely baked.

Step 5

Remove cakes from the oven and allow to cool while you prepare the filling and frosting.

Step 6

In the bowl of a stand mixer fitted with the whisk attachment, add the two cups heavy whipping cream and half a cup of milk. Begin whipping your cream, and then add in the powdered pudding mix. Whip the mixture until the ingredients are combined, and then increase the speed to whip the mixture into a thick mousse.

Step 7

For the buttercream frosting, add the softened sticks of butter to the mixer fitted with the paddle attachment. Whip the butter until smooth and gradually add in two cups of powdered sugar while the mixer is running. Gradually add in half a cup of milk. Add in four teaspoons vanilla extract. Continue to gradually add in the rest of the powdered sugar while the mixer is running, scraping down the sides of the bowl with a spatula as needed. Once all ingredients are incorporated and your frosting begins to form, increase the speed of the mixer to whip the frosting.

Step 8

Fill the cake by placing one cake layer on a cardboard cake board or platter. Cover the first layer with the mousse filling, and then top it with the second cake layer. Frost the top and sides of your cake, and decorate as desired.