Crush cookies either with food processor or hand crushed in sealed plastic bag. Do not over process.
Melt 4 tablespoons butter.
Combine crushed cookies and melted butter (either in food processor or in bag).
Press cookie mixture into 9 inch round dish on bottom and sides. Freeze until hardened, at least 20 minutes.
Spread slightly softened ice cream over crust. Cover and freeze again, at least 30 minutes.
Make chocolate sauce: combine remaining 1/2 tablespoon butter, chocolate chips, and milk. Melt on stove or in microwave (about 30 seconds). Allow to cool completely.
Drizzle chocolate sauce over ice cream pie. Add optional decorations (see ideas below).
Before covering, consider placing toothpicks around pie so that cover or plastic wrap doesn't touch pie top and smear decorations. Cover and freeze until solid, at least 3 hours, ideally overnight.
Let stand at room temperature for 5-10 minutes before cutting. Slice pie into wedges and serve.
Video
Notes
Pie can be made 3 days ahead.Topping ideas:
Oreo cookies over cookies & cream ice cream
Candy canes or Thin Mint Cookies over mint chip ice cream
Unreal peanut butter cups on top of chocolate peanut butter ice cream
Fruit or chocolate chips on top of vanilla or fruit-flavored ice cream
Freeze leftovers for up to 6 months in air tight container.