Bake cake mix according to package directions for two 9 inch round cakes. Let cool, and remove from pans.
Remove ice cream from the freezer and let it partially thaw (you don't want it to be melted, but it does need to be spreadable).
On a freezer-safe plate, place one 9 inch cake. Measure a piece of wax paper, folded in half, to go around the circumference of the cake and secure in place with tape (this will help the cake keep it shape until you're ready to serve). On top of the cake, evenly spread ice cream to the edges, pressing it up against the wax paper.
Crumble two-thirds of the package of cookies, and sprinkle evenly over the ice cream. Place the second 9 inch cake on top of the cookie crumbs, and press down gently (don't push too hard, or your wax paper may come undone).
Freeze for 2-3 hours, until ice cream can hold it's shape
Before serving, heat chocolate chips and butter in a saucepan over medium heat, stirring until smooth. Remove wax paper from the cake, then pour chocolate sauce over the top, letting it drip down the sides. Top cake with remaining chocolate chip cookies, and serve immediately.