1-Step 1: Prep the pan and oven Start by preheating your oven to 350°F. Grease a 9×13-inch baking pan, then line it with parchment paper if you want easier lifting after baking. If you plan to turn this into a cookies and cream sheet cake for a crowd, you can use a larger sheet pan and adjust baking time as needed.

2-Step 2: Mix the dry ingredients In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt. This helps the leaveners spread evenly through the batter, which is key for a soft and even bake. Set the bowl aside while you work on the wet ingredients.

3-Step 3: Cream the butter and sugar In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy, about 2 to 3 minutes. This step adds air to the batter, which helps the cake stay tender. Scrape down the bowl as needed so everything blends well.

4-Step 4: Add the egg whites and vanilla Mix in the egg whites one at a time, beating well after each addition. Then add the tablespoon of vanilla extract. The batter may look slightly curdled at this stage, but that is normal and will smooth out once the remaining ingredients go in.

5-Step 5: Add sour cream and milk Stir in the sour cream, then add half of the dry mixture. Pour in the whole milk, followed by the rest of the dry ingredients. Mix gently and stop as soon as the batter comes together. Overmixing can make the cake dense instead of light and soft.

6-Step 6: Fold in the cookies Gently fold in the 1 and 1/4 cups chopped chocolate sandwich cookies. Try not to crush them too much, because small cookie chunks create little pockets of flavor in the cake. This is what gives the oreo cake its classic cookies and cream look.

7-Step 7: Bake the cake Spread the batter evenly in the prepared pan and smooth the top with a spatula. Bake for 24 to 30 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs. If you are using a slightly larger pan, begin checking a few minutes early.

8-Step 8: Cool completely Set the pan on a wire rack and let the cake cool fully before frosting. A warm cake can melt the whipped cream frosting, so patience matters here. If you are baking ahead for a busy day, you can cool the cake, cover it, and frost it later.

9-Step 9: Make the frosting Beat the softened cream cheese and confectioners’ sugar together until smooth. Add the vanilla extract, then pour in the cold heavy cream. Whip until the frosting becomes fluffy and holds soft peaks. Fold in the chopped chocolate sandwich cookies by hand so you keep nice cookie pieces throughout the frosting.

10-Step 10: Frost and finish Spread the frosting over the cooled cake in an even layer. If you want a fuller look, swirl the top with a spoon or offset spatula. Finish with optional chocolate sandwich cookies for garnish, then chill briefly before slicing for cleaner pieces.