Preheat oven to 350°F. Line three 8-inch pans with circles of parchment paper on the bottom and spray with baking spray.
Combine sugar, oil, and butter in a large bowl. Beat on medium-high speed for 2-3 minutes until creamy and light.
1 3/4 cups granulated sugar, 1/2 cup vegetable oil, 1/4 cup salted butter
Add the egg whites one at a time, beating well on medium speed and scraping the bottom and sides of the bowl with a spatula occasionally to make sure everything is mixing together evenly.
4 egg whites
Add the sour cream and vanilla extract. Mix again until combined.
3/4 cup sour cream, 2 teaspoons vanilla extract
Add half of the flour along with the baking powder, baking soda, and salt. Mix on low speed just until mostly combined. Add the milk and mix again, followed by the remaining flour.
2 1/2 cups all-purpose flour, 2 teaspoons baking powder, 1/2 teaspoon baking soda, 1 teaspoon salt, 3/4 cup whole milk
Use a spatula to fold in the broken up Oreos. Divide the batter evenly between the three pans (it should be about 2 cups of batter per pan).
16 Oreos
Bake for 25-30 minutes until a toothpick or skewer inserted in the center of each cake comes out clean or with just a few crumbs on it. You can also bounce your finger on the top of the cake and it should spring right back.
Let the cakes cool for 5-10 minutes in the pans, then run a thin, sharp knife around the edges of the pan and invert them onto wire racks to cool completely.