1. For the Mexican chocolate ganache, put the chocolate in a heatproof bowl. Bring the cream just to a boil in a small pan. Pour immediately over the chocolate and let sit for a minute or 2. Whisk until the chocolate is melted and the ganache is completely smooth. Set aside to cool.
2. For the ice cream sandwiches, break the graham crackers in half. Put the candied walnuts on a small plate. Turn the pint of ice cream on its side and use a serrated knife to slice through the carton, creating 6 ice cream discs.
3. Spread some of the Mexican chocolate ganache on each graham cracker half. Add an ice cream disc (remove the carton) to 6 of the graham cracker halves and top with the remaining graham crackers. Roll the edges in the candied walnuts. Serve immediately.