Line a six-inch springform pan with parchment paper, adding a parchment or acetate strip around the inside edge if desired. Crush eight sandwich cookies into fine crumbs, mix them with the melted butter, and press firmly into the pan; freeze for 15–20 minutes.

Soften the chocolate ice cream until spreadable but still firm enough to hold its shape. Spread it evenly over the chilled crust and freeze for about 30 minutes.

Stir the cooled hot fudge sauce together with the 1/2 cup finely crushed cookies. Spread the fudge-and-cookie mixture over the chocolate ice cream in an even layer.

Soften the vanilla ice cream until spreadable, then spoon it over the fudge-crunch center and smooth the top. Cover the pan and freeze for at least 4–6 hours, preferably overnight, until completely firm.

Remove the frozen cake from the springform pan and peel away the parchment or acetate. Frost the top and sides with whipped topping or lightly sweetened whipped cream, then decorate with sprinkles, cookie crumbs, chocolate curls, or optional fudge.

Let the cake stand at room temperature for 10–15 minutes before slicing. Warm a sharp knife under hot water, dry it carefully, and cut immediately; rewarm and dry the knife between slices for clean layers.