Step 1

Preheat your oven to 325 degrees F. Spray three 8-inch or four 6-inch round cake pans with non-stick spray and then line with parchment. Spray again. Set aside.

Step 2

In a medium sized mixing bowl, whisk together the cake flour, baking powder and salt. Set aside.

Step 3

In the bowl of an electric mixer, fitted with the paddle attachment, cream the butter and the sugar for two minutes on medium-high speed.

Step 4

Scrape down the sides of the bowl and begin to add the egg whites on medium speed, scraping down the sides and bottom of the bowl between addition.

Step 5

Add the sour cream and vanilla extract and beat until incorporated, about one minute.

Step 6

With the mixer on low speed, add 1/3 of the flour mixture, followed by 1/2 cup of the buttermilk. Repeat the additions, 1/3 flour mixture, 1/2 cup buttermilk and the final 1/3 flour mixture. Only mix until the flour mixture is incorporated, about 30 seconds. Scrape down the sides and bottom of the bowl and mix again for another 20 to 30 seconds on low.

Step 7

Pour about 18 ounces of cake batter into each of the three 8-inch cake pans or 13 ounces in each of the 6-inch pans and bake for 25 to 28 minutes, or until a toothpick inserted into the center of the cake comes out with a few moist crumbs on it. Let cool in the pans for about 15 minutes and then invert onto a wire rack to cool completely. (Tip: spray your wire cooling racks with nonstick spray).

Step 8

In the bowl of a stand mixer fitted with the whisk attachment, whisk the heavy whipping cream on high for about 3 to 5 minutes, until the cream forms stiff peaks. Transfer the cream to another bowl and set aside.

Step 9

In the now empty bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese for a couple minutes until smooth. Gradually add the powdered sugar. Beat for a couple minutes until smooth.

Step 10

Fold in the whipped cream until no streaks of whipping cream remain.

Step 11

Best to make right before you assemble the cake so the cookies don't get soggy. If you want to make this ahead of time, just leave out the Oreos until you're ready to assemble.

Step 12

In the bowl of an electric mixer, fitted with the paddle attachment, beat the butter for about 2 minutes, until light and fluffy and pale in color.

Step 13

With the mixer on slow, gradually add the powdered sugar, followed by the heavy cream, vanilla and pinch of salt.

Step 14

Once all of the ingredients are combined, turn the mixer to medium-high and beat for about 3 to 5 minutes. Scrape down the sides of the bowl and beat for a couple minutes more.

Step 15

Before using the buttercream, make sure to beat it by hand with a wooden spoon or large spatula to help push out the air pockets.

Step 16

Place the first cake layer top side up, in the center of the cake board. Pipe a rim of buttercream around the edge of the cake and then fill the center with about 1 cup of the filling.

Step 17

Place the second cake layer on top of the buttercream and filling. Repeat piping and filling.

Step 18

Place final cake layer, top side down.

Step 19

Crumb coat the entire cake with a thin layer of the buttercream and freeze for about 10 to 15 minutes to set this layer of frosting.

Step 20

Once the crumb coat is set, continue to frost the cake with the remaining buttercream.