Set aside 2 peanut butter cup chocolate chip cookies to crumble on top of the pie.
Place the milk in a measuring cup. Dunk 6-8 cookies quickly, one at a time, in the milk and place in a single layer in the bottom of the graham cracker crust. Spread 1/2 of the Cool Whip evenly over the cookies.
Dip 8-10 cookies, one at a time quickly, in the remaining milk and place in a single layer over the Cool Whip layer. Spread the remaining 1/2 of the Cool Whip evenly over the cookies.
Crumble the reserved 2 cookies and sprinkle on top of the pie. Cover and chill in the refrigerator for at least 8 hours before serving.