Preheat the oven to 325 degrees.
Grease and flour two 8 inch round (2 inch deep) cake pans.
Add 15-20 oreos to a ziplock gallon bag. Push the air out and seal it. Take a meat mallot or a roller and hit the oreos chopping them up. You don't need to crush them, just chop them up well. Set aside.
In a bowl, mix together the sour cream, milk, vanilla extract and egg whites.
Whisk until smooth and set aside.
In a large mixing bowl, add the flour, sugar, baking soda, baking powder and salt.
Whisk together.
Turn on the mixer to medium speed and add the shortening and butter in chunks to the flour mixture. (If you don’t have a stand mixer, you can use a hand mixer.) Once all the butter and shortening has been added, turn the mixer on medium high and mix until all the flour is coated. The mixture should be crumbly with a sand-like texture.
Add in half the liquid mixture and mix on medium speed just until well combined. Don't mix too long or it will whip the egg whites and make the cake spongy.
Scrape down the sides and bottom of the bowl and add in the last half of the liquid mixture. Mix on medium speed just until the ingredients are combined, about 30 seconds. Be careful not to over-mix the batter at this point or your cake will turn out dry and dense.
Scrape down the sides of the bowl and then mix again on medium, only for about 10-15 seconds.
Add the chopped Oreos and mix them in by hand with a large spoon or spatula.
Pour into the greased and floured cake pans and bake at 325 degrees for approximately 45 minutes.A toothpick inserted into the middle should come out with a few moist crumbs.
Once baked, set the cake layers in their pans on cooling racks for about 10 minutes, then turn the cakes out of the pans and cool on the racks completely before adding frosting.