1-First Step: Prepare Your Equipment and Pan Preheat your oven to 350°F (177°C). Grease a 9×13 inch cake pan thoroughly with butter or non-stick spray. For extra insurance against sticking, consider lining the bottom with parchment paper. This step takes about 5 minutes and ensures your cake releases cleanly after baking.

2-Second Step: Mix the Dry Ingredients In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt. Set this mixture aside while you prepare the wet ingredients. This ensures even distribution of the leavening agents and prevents any pockets of baking powder or soda in the finished cake.

3-Third Step: Cream Butter and Sugar Using a stand mixer fitted with the paddle attachment or a hand mixer, beat the softened butter on medium speed until smooth and creamy, about 1 minute. Add the granulated sugar and continue beating until the mixture is combined and slightly fluffy roughly 2-3 minutes. The mixture won’t become dramatically lighter since we’re using egg whites rather than whole eggs.

4-Fourth Step: Add Wet Ingredients Add the egg whites and beat until combined, scraping down the sides of the bowl as needed. Next, beat in the sour cream and vanilla extract until the mixture is uniform. The batter may look slightly curdled at this stage, which is perfectly normal due to the high liquid content from the egg whites and sour cream.

5-Fifth Step: Combine Wet and Dry Ingredients With the mixer on low speed, gradually add the dry ingredient mixture to the wet ingredients. Mix just until combined avoid overmixing as this develops gluten and creates a tough cake. With the mixer still running on low, slowly pour in the room temperature whole milk. Continue mixing only until the milk is incorporated and the batter is smooth.

6-Sixth Step: Fold in the Cookies Using a rubber spatula, gently fold in the 1 and 1/4 cups of chopped chocolate sandwich cookies. Work with light, folding motions rather than stirring vigorously to distribute the cookies evenly without deflating the batter. Be careful not to overmix at this stage.

7-Seventh Step: Bake the Cake Pour the batter into your prepared 9×13 inch pan, spreading it into an even layer. Bake for 32-35 minutes, or until a toothpick inserted into the center comes out clean. The cake should spring back when lightly touched and the edges will begin pulling slightly away from the pan. Every oven bakes differently, so start checking at the 30-minute mark.

8-Eighth Step: Cool Completely Allow the cake to cool completely in the pan on a wire rack before frosting. This typically takes 1-2 hours. Attempting to frost a warm cake will cause the whipped cream frosting to melt and slide off, ruining your presentation.

9-Ninth Step: Prepare the Whipped Cream Frosting While the cake cools, make the frosting. Beat the softened cream cheese in a large bowl until completely smooth with no lumps remaining. Add the confectioners’ sugar and vanilla extract, beating until smooth and creamy. Cream cheese provides protein and calcium while creating a stable base for the whipped cream. With the mixer on low speed, slowly pour in the cold heavy cream. Once all the cream is incorporated, increase the speed to high and beat until stiff peaks form this typically takes 2-3 minutes. Watch carefully to avoid overbeating, which can cause the mixture to separate.

10-Tenth Step: Finish and Serve Reserve about 1 cup of the plain frosting for piping decorations if desired. Fold the remaining 1 cup of chopped chocolate sandwich cookies into the rest of the frosting using gentle folding motions. Spread the cookie-studded frosting evenly over the cooled cake. If you reserved plain frosting, pipe decorative borders or patterns around the edges. Garnish with additional whole or mini cookies if desired. Serve immediately, or refrigerate for up to 1 day. Allow refrigerated cake to come to room temperature for 30-60 minutes before serving for the best texture and flavor.