How to Make It
Line a 9- x 5-inch loaf pan with parchment paper or plastic wrap, leaving 1-inch overhang on long ends as handles.
Beat heavy cream, powdered sugar, and vanilla with an electric mixer on medium-high speed until stiff peaks form, about 5 minutes.
Arrange 4 1/2 ice cream sandwiches in a single layer on bottom of prepared loaf pan, cutting sandwiches as needed to fit evenly. Dollop with 1 cup of the whipped cream mixture, spreading to evenly cover sandwich layer. Top with remaining 4 1/2 ice cream sandwiches; spread 1/2 cup of the whipped cream mixture to cover sandwich layer. Cover with plastic wrap; freeze at least 2 hours or up to 4 hours. (Refrigerate remaining whipped cream mixture until ready to use.)
Remove plastic wrap from cake. Using parchment handles, lift and remove cake from loaf pan; invert cake onto a large plate. Spread sides and top of cake with remaining whipped cream. Drizzle with chocolate syrup, and sprinkle with crushed cookies.
Make ahead: To assemble and freeze the cake 4 to 24 hours in advance of serving: In Step 2, beat 3/4 cup of the heavy cream and 1 tablespoon of the powdered sugar until stiff peaks form. Assemble the cake as instructed in Step 3 (using all of the whipped cream), then cover and freeze cake up to 24 hours. When ready to serve, beat remaining 1 1/4 cups heavy cream, remaining 2 tablespoons powdered sugar, and the 1/4 teaspoon vanilla until stiff peaks form. Use freshly whipped cream to complete cake as instructed in Step 4.