Step 1: Prepare the oven and pans
Preheat the oven to 325°F (160°C).
Grease and flour two 8-inch round cake pans thoroughly.
Place parchment paper rounds in the bottom of each pan for easy release.

Step 2: Crush the Oreos
Add about 15-20 Oreos to a ziplock gallon bag, push the air out, and seal it.
Use a meat mallet or a rolling pin to chop the Oreos into small pieces.
Do not crush them into fine crumbs; leave some chunks for texture.

Step 3: Mix the wet ingredients
In a medium bowl, whisk together the sour cream, milk, vanilla extract, and egg whites until smooth.
Set aside this mixture for later.
This helps to ensure even mixing when combined with the dry ingredients.

Step 4: Mix the dry ingredients
In a large mixing bowl, add the cake flour, sugar, baking soda, baking powder, and salt.
Whisk together until well combined.
This aerates the flour and helps distribute the leavening agents evenly.

Step 5: Add the fats to the dry mixture
With the mixer on medium speed, add the shortening and butter in chunks to the dry mixture.
Mix until the flour is coated and the mixture resembles coarse sand.
This step is critical for a tender crumb.

Step 6: Combine wet and dry ingredients
Add half of the liquid mixture to the flour mixture and mix on medium speed just until combined.
Scrape down the sides of the bowl, then add the remaining wet mixture.
Mix just until the ingredients are incorporated, being careful not to over-mix.

Step 7: Fold in the chopped Oreos
Use a spatula to gently fold the chopped Oreos into the batter by hand.
This keeps the batter light and prevents the Oreos from breaking down too much.
Distribute them evenly throughout the batter.

Step 8: Bake the cake
Pour the batter evenly into the prepared pans and smooth the tops.
Bake at 325°F for about 45 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the cakes to cool in the pans for 10 minutes before turning them out onto wire racks.

Step 9: Prepare the Oreo frosting
Crush about 10 Oreos finely, using a ziplock bag or a food processor.
In a large mixing bowl, beat the butter, cream cheese, and salt until smooth and creamy.
Gradually add the confectioner’s sugar, milk, and vanilla extract, mixing well after each addition.
Stir in the finely crushed Oreos with a spatula.

Step 10: Assemble the cake
Place one cake layer on a serving plate or cake stand.
Spread a generous layer of frosting over the top.
Place the second cake layer on top and frost the top and sides of the entire cake.

Step 11: Decorate the cake
Press crushed Oreos around the bottom edge of the cake.
Use a piping bag fitted with a large star tip to pipe swirls of frosting on the top.
Garnish with mini Oreos or extra crushed Oreos for a fun finish.