1-First Step: Prepare the pan and oven Start by preheating your oven to 350°F. Grease a 9 by 13-inch pan well, then line the bottom with parchment paper if you want easier release. This helps the Oreo sheet cake lift out cleanly after baking and keeps the edges from sticking. If you are making this for a party, you can also use an 18 by 13-inch half sheet pan, but the bake time will be shorter.

2-Second Step: Mix the dry ingredients In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt. Mixing these ingredients first helps them spread evenly through the batter, so the cake rises nicely and bakes with a smooth crumb. Set the bowl aside while you work on the wet ingredients.

3-Third Step: Cream the butter and sugar In a large bowl, beat the softened butter and granulated sugar together until the mixture looks pale and fluffy. This step usually takes 2 to 3 minutes with a hand mixer or stand mixer. Beating air into the butter is important because it helps the Oreo sheet cake stay light instead of dense. If you are baking for a special event, do not rush this part.

4-Fourth Step: Add the egg whites and vanilla Beat in the egg whites one at a time, mixing well after each addition. Room temperature egg whites blend more smoothly and help the batter hold air better. Then mix in the vanilla extract. The batter may look slightly curdled at this stage, but that is normal and it will come together once the dry ingredients and milk are added.

5-Fifth Step: Add the sour cream and milk Mix in the sour cream until fully blended, then add the dry ingredients in three parts, alternating with the milk. Start and end with the dry ingredients for the best texture. Mix on low speed just until combined, because overmixing can make the cake tough. At this point, the batter should look thick, smooth, and rich.

6-Sixth Step: Fold in the chopped cookies Use a spatula to gently fold in the chopped chocolate sandwich cookies. This gives the Oreo sheet cake its signature cookies and cream look and adds little crunchy bites throughout the cake. If you want a lighter texture, chop the cookies into small pieces instead of very fine crumbs. For extra cookie flavor, reserve a few pieces for the top before baking.

7-Seventh Step: Bake the cake Spread the batter evenly into the prepared pan and smooth the top with a spatula. Bake at 350°F for about 28 to 34 minutes for a 9 by 13-inch pan, or until a toothpick inserted in the center comes out mostly clean with a few moist crumbs. If using a half sheet pan, start checking earlier, around 18 to 22 minutes. The top should look set and lightly golden.

8-Eighth Step: Cool completely Let the cake cool in the pan for about 20 minutes, then move it to a wire rack if you prefer faster cooling. The cake must be fully cool before frosting, or the whipped cream frosting can melt. This part takes patience, but it helps the finished dessert look neat and taste better.

9-Ninth Step: Make the whipped cream frosting In a large bowl, beat the softened cream cheese, confectioners’ sugar, and vanilla extract until smooth. In a separate bowl, whip the cold heavy cream until stiff peaks form. Gently fold the whipped cream into the cream cheese mixture until fully combined. Finally, fold in the chopped chocolate sandwich cookies. The result should be fluffy, creamy, and easy to spread.

10-Tenth Step: Frost and finish Spread the frosting over the cooled cake in an even layer. Use the back of a spoon or an offset spatula to create soft swirls on top. Garnish with mini or regular chocolate sandwich cookies if you like a more finished look. Chill the cake for 20 to 30 minutes before slicing if you want cleaner cuts.

11-Final Step: Slice and serve Cut the Oreo sheet cake into squares and serve chilled or slightly cool. It pairs well with cold milk, coffee, or even a scoop of vanilla ice cream. Because the frosting is light and the cake is soft, this dessert works well for family dinners, birthday tables, and casual gatherings.