Special equipment: two 9-inch square metal cake pans
Grease two 9-inch square metal cake pans with nonstick cooking spray. Prepare and bake the red velvet cake in the greased cake pans according to the package instructions. Cool the cakes in the pans on wire racks for 15 minutes, then unmold the cakes onto the racks and let cool completely. Trim off the tops of the cakes to yield two 1/2-inch-high cakes.
Arrange 9 of the ice cream sandwiches into a 9-inch square on a platter, trimming the sandwiches as needed to form the square. Top with one of the cake layers. Arrange another layer of 9 ice cream sandwiches on top of the cake layer. Repeat with the remaining layer of cake and 9 ice cream sandwiches. Chill in the freezer while you prepare the topping.
Combine the cream, sugar, food coloring and vanilla if using and beat until stiff peaks form. Using an offset spatula, generously frost the cake on all sides with the whipped topping. Decorate the cake with sprinkles as desired. Place in the freezer until ready to serve.