Preheat oven to 350 degrees. Line two muffin tins with 24 paper muffin cups. Using a sharp knife, split 24 Oreos into halves leaving cream filling attached to one side (save filling free cookie sides to crush and sprinkle over frosted cupcakes). Place 1 Oreo half, with cream filling side up, at the bottom of each muffin cup, set aside.
In mixing bowl, whisk together flour, baking powder and salt, set aside. In a separate large mixing bowl, using an electric hand mixer on medium speed, whip together butter and sugar until pale and fluffy, about 3 - 4 minutes. Add in egg whites, one at a time, mixing until combine after each addition. Measure 3/4 cup milk into a liquid measuring cup, then add sour cream and vanilla to milk and whisk to combine.
Working in two separate batches, add flour mixture followed by milk mixture to butter mixture, and mix just until combine after each addition. Fold in 16 chopped Oreos. Evenly divide batter among prepared muffins cups (pouring it over the tops of the Oreo halves), filling each cup about 2/3 full. Bake in preheated oven about 23 - 26 minutes until toothpick inserted into center of cupcake comes out clean. Allow to cool 5 minutes before transferring to a wire rack to cool completely.
Once cupcakes have cooled completely, frost with Fluffy Cream Cheese Frosting. Finely crush about half of the cream filling free cookie sides and sprinkles over cupcakes then garnish cupcakes with optional cookie halves (you could even use the remaining 12 cookie halves). Store cupcakes in an airtight container.
Fluffy Cream Cheese Frosting
In a large mixing bowl, using an electric hand mixer on medium speed, whip together butter and cream cheese until fluffy about 1 minute. Stir in sour cream and vanilla. Add in powdered sugar and mix until smooth, light and fluffy, about 3 minutes.
Recipe Source: cupcake adapted from Beantown Baker, frosting Cooking Classy