Line a rimmed baking sheet with wax paper or parchment paper.
Melt 1 1/2 cups of milk chocolate chips and pour over the lined pan, spreading evenly. Refrigerate for 30 minutes until hardened.
Melt the white chocolate chips, mix with vegan marshmallows fluff, and spread over the hardened milk chocolate layer. Refrigerate for 30 minutes.
Crumble graham cracker sheets and sprinkle over the marshmallow layer, pressing down slightly. Refrigerate for 30 minutes.
Melt 2 cups of milk chocolate chips and spread over the graham cracker layer. Freeze for 2 hours.
Break the bark into pieces of desired size.
Store leftovers in an airtight container in the refrigerator.