Line a 9x13 dish with graham crackers, covering the base as much as possible. It is okay if there are gaps.
Pour 1 1/2 bags of chocolate chips into a microwave-safe bowl. Microwave in 30-second increments, stirring gently after every 30 seconds, until chocolate is fully melted. Be careful not to overheat or over-mix, as chocolate will get dry and crumbly. It took me about three 30-second increments (approx. 1 1/2 minutes) for a full, creamy melt.
Pour melted chocolate into your dish on top of the graham crackers, spreading into an even layer. Refrigerate for 10-15 minutes or until chocolate has hardened.
Pour 2 bags of white chocolate chips into a microwave-safe bowl, and repeat the same process as you did with the chocolate chips, heating in 30-second increments until melted.
When the white chocolate has fully melted, gently stir in 1/2 tsp of peppermint extract. Pour over top of your dish with the hardened graham crackers and chocolate, and spread into an even layer. Refrigerate for 10-15 minutes or until white chocolate has hardened.
(Skip this step if you are using store-bought crushed candy cane topping.) While the white chocolate layer is hardening, crush your candy canes into small pieces using a mortar and pestle. Make sure pieces are bite-sized so they are easy to consume.
(Note: this layer is optional.) Then, pour the remaining 1 1/2 bags of chocolate chips into a microwave-safe bowl, and repeat the melting process by heating in 30-second increments.
Pour melted chocolate in the dish with the hardened graham cracker and chocolate layers, and spread into an even layer. Before you place your dish back into the refrigerator, sprinkle with crushed candy canes and break remaining graham crackers and crumble over the top.
Place the dish back in the refrigerator and let everything harden.
Once your bark has set, break into small pieces using a knife. Since I made my bark in three layers, it was a bit thick to cut, so I used a hammer to break it into smaller pieces.