Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9 inch round cake pans.
In a large bowl, mix the cake mix, water, oil, and 3 egg whites with an electric mixer on high speed for 2 minutes. Gently stir in crushed cookies. Pour batter into the prepared pans.
Bake for 25 to 35 minutes in the preheated oven, or until a knife inserted in the center of the cake comes out clean. Cool 10 minutes in pans. Remove from pans, and completely cool on racks.
To Make Frosting: In a small bowl, thoroughly blend the 1/2 cup confectioners' sugar, shortening, vanilla, and 2 egg whites. Beat in remaining confectioners' sugar until creamy. Frost the cake, and garnish with remaining cookies.