Step 1 Prepare the pan. Very lightly butter the bottom and sides of the pan. Line the bottom of the pan with parchment paper and the sides with the cake collars or parchment paper.
Step 2 In a medium bowl, combine the chocolate cookie crumbs and melted butter. Using a spatula or your hands, work the butter and crumbs until well-combined.
Step 3Press the cookie mixture into the base of the pan, pressing it firmly to the base. Smooth around the base of the pan with the back of a spoon to form a level crust, and brush any spare crumbs from the sides of the pan. Place the pan in the freezer until ready to add a layer of mousse.