Line the springform base with parchment. Combine crust crumbs and melted butter, press firmly across the base, and freeze for 20 minutes.
Let vanilla ice cream soften just until spreadable, not melted. Spread over the frozen crust in an even layer and freeze for 1 hour.
Spread cold thick fudge sauce over the firm vanilla layer. Scatter crushed cookies over the sauce, leaving the outer edge reasonably clear.
Soften chocolate ice cream slightly and spread carefully over the cookie layer. Press gently to remove large gaps without melting the layer below.
Cover tightly and freeze at least 6 hours until solid. Keep the pan level so the layered cross-section is even.
Whip heavy cream, powdered sugar, and vanilla to stiff peaks. Release the frozen cake from the ring, supporting the base securely.
Spread whipped cream over the top and sides, working quickly. Freeze another 30–60 minutes to set the coating before cutting.
Let stand 5–10 minutes, then slice with a warm dry knife, wiping between cuts. Return remaining cake to the freezer promptly after serving.
