Preheat the oven to 350 degrees Fahrenheit. Line a standard muffin pan with muffin liners, set the pan aside.
Add the flour, baking powder, and salt to a medium sized bowl and whisk them together. Set them aside.
In a large bowl, add the granulated sugar, and butter and mix them together with an electric mixer (a stand mixer or hand mixer) for 1-2 minutes.
Add in the egg whites, sour cream, and vanilla extract and mix them in until they are just combined. Scrape down the bottom and sides of the bowl as needed.
Add in half the dry ingredients, and mix until mostly combined.
Add in the buttermilk and mix until combined. The batter may look curdled, but that's okay.
Add in the remaining dry ingredients, and mix until combined.
Add in the chopped Oreos and gently fold them into the batter.
Fill the cupcake liners each about 3/4 full, filling the 12 spots evenly.
Bake the cupcakes for 16 to 20 minutes or until a toothpick inserted in the center comes out clean, or with a few moist crumbs.
Let the cupcakes cool for a few minutes in the muffin pan, then transfer them to a cooling rack to cool completely.