Preheat the oven to 350º F. Spray a 9x13 inch pan with non-stick cooking spray.

In a mixing bowl combine the butter and sugar, beat using an electric mixer, 1-2 minutes until fluffy. Add in the egg whites, mixing with the mixer about 30 seconds. Add in the sour cream, milk, and vanilla extract. Beat lightly with the electric mixer. In a separate mixing bowl combine the flour, baking soda, and salt. Gradually add the flour mixture to the wet ingredients a few spoonfuls at a time. Add in the crushed oreos. Mix until just incorporated. Pour the batter into the pan and spread evenly.

Bake for 40-44 minutes or until a few moist crumbs remain on a toothpick when inserted into the center. Allow the cake to cool completely before adding the frosting. I baked my cake in a glass pan, which is slower to heat up, meaning the baking time for a glass pan is longer than it would be for a metal pan. Those of you who have made this recipe in a metal pan are reported that 30 minutes was a good bake time for a metal pan. Remember, every oven and pan is different!

In a mixing bowl, beat the butter with an electric mixer until fluffy. Add in the vanilla extract. Begin to add the powdered sugar, about 1 cup at a time, mixing by hand. Continue adding powdered sugar until the frosting no longer looks wet and tastes good to you. Add in the finely blended oreos (I like to call it "oreo flour"). Then I use my electric mixer one last time to make sure the powdered sugar is really incorporated and ready to go. If the frosting becomes too thick, add a dash of milk or heavy cream.

Spread the buttercream on top of the cake. Be sure to reserve some buttercream for swirls to top the cake if you’d like.

For an extra fancy presentation, after I evenly spread the cookies & cream buttercream over the cake, I lightly sprinkled oreo crumbs on the top. Then I cut the cake into squares and in the center of each piece, I added a buttercream swirl and a mini oreo.