In a large mixing bowl, combine cake mix, milk, butter and eggs. Beat on low speed until moistened; beat on high speed for 2 minutes. Gently fold in crushed cookies. Pour into two greased and floured 8 inch round cake pans. Bake at 350 °F for 30 minutes or until a wooden toothpick inserted in the center comes out clean. Cool for 10 minutes; remove from pans to wire rack to cool completely. In a mixing bowl, beat sugar, butter, milk and vanilla until smooth. Frost cake. If desired, decorate the top with cookies halves and the sides with crushed cookies.