Step 1

Preheat the oven to 350°F. Grease two identical 9x13-inch baking pans line the bottoms with parchment paper. Lightly grease the parchment paper.

Step 2

In the bowl of an electric mixer (stand mixer preferred) combine the cake flour, sugar, baking powder, and salt. Whisk to combine.

Step 3

Add the butter to the flour and mix until well incorporated and crumbly, with a texture similar to damp sand or cornmeal. The mixture may also form a paste in humid conditions, this is fine too.

Step 4

With the mixer running on low speed, add the egg whites and the whole eggs, one at a time, beating well after each addition. Scrape down the bowl and mix again briefly.

Step 5

Add the milk, about 1/3 at a time, to the batter. Beat 1-2 minutes after each addition. Mix in the vanilla extract.

Step 6

Divide the batter evenly between the prepared pans. Bake for 26-30 minutes, or until the cakes are golden on top, and a toothpick tester inserted near the center comes out clean. Let cakes cool for 5 minutes in the pan, then turn them out onto wire cooling racks to cool completely. Peel away the parchment paper and discard it.

Step 7

Optional step: Wrap and refrigerate cakes for 2 hours, or overnight. This will firm the crumb and make them easier to level.

Step 8

When cakes are completely cool, level the rounded tops using a serrated knife.

Step 9

In the bowl of an electric mixer fitted with the whisk attachment, beat the cream cheese until smooth. Add the powdered sugar and mix again until incorporated.

Step 10

Add the heavy cream and mix on low until incorporated. Scrape down the bowl and mix again, raising the speed slightly, until the mixture is smooth (you’re not trying to whip the cream, just mix until the two are smooth).

Step 11

Add the whole milk; beat to combine Then, add the dry instant vanilla pudding powder. Mix until combined. Scrape down the bowl (sides and bottom) and mix on medium-high speed until the mixture thickens, 2-3 minutes.

Step 12

Place a white cake layer on a cake board or serving platter and top with all of the cream cheese mousse. Spread evenly to the edges and top with the second white cake layer. Cover and refrigerate while you make the buttercream.

Step 13

In the bowl of an electric mixer fitted with the whip attachment, add the butter and mix until creamy. Add three cups of powdered sugar; mix on low speed until combined, the beat on high speed 1 minute. Add remaining confectioners’ sugar, pulsing the mixer on and off to combine slowly, so the sugar doesn’t fly out of the mixing bowl. Beat until incorporated. Add milk or cream a little at a time to thin. Mix on high speed for 5 minutes, or until lightened in color and billowy. The frosting should lose most of it yellow butter hue.

Step 14

Transfer about 1 1/4 cups of the buttercream to a piping bag fitted with a large open star tip; set aside Use the remaining frosting to cover the entire cake, smoothing it evenly with an offset spatula.

Step 15

Use the piping bag with the decorator tip to pipe a shell border around the bottom edge of the cake (see video for this action). If using sprinkles, add them after you pipe one edge (wait too long and the sprinkles won’t stick!). Pipe a shell border on the top edge of the cake and add decors, if using.

Step 16

Refrigerate cake until the buttercream is set, then cover gently with plastic wrap. Store cake in the refrigerator.

Step 17

Bring the cake to room temperature before serving. The cake’s texture, flavor, and filling will be most developed at room temperature.