To build the sandwiches, lightly spray two 9" x 5" loaf pans with pan spray. Line the pans on all sides with plastic wrap.
Cut two pieces of the graham cake to fit on the bottom of the loaf pans. Gently press the cake into the bottom of the pans so thy fit snuggly into the pan.
Make the chocolate ganache and set it aside to cool. The ganache should be thick but still pourable when you use it. Pour half of the ganache onto each piece of cake in the loaf pans. Transfer the pans to the freezer to firm up, at least 4 hours and up to overnight.
Prepare the Toasted Marshmallow Ice Cream and when ready to extrude the ice cream from the machine spread it directly onto only one of the loaf pans with cake and ganache. Transfer the pan to the freezer for about an hour.
Once the ice cream has begun to set, remove the pan without the ice cream. Gently lift the cake and ganache out of the pan and place on top of the ice cream, chocolate side down. Press down to sandwich the two sides together. Wrap the loaf in plastic and return it to the freezer until you are ready to use it.
To serve the sandwiches, remove the pan from the freezer, and slide the loaf out of the pan onto a clean cutting surface. Trim the edges and then cut the cake into 1 1/2 inch bars.
Serve with the Fireball Whisky Sauce.