Grease an 8x8-inch baking pan with butter or line it with parchment paper.

Combine 2 cups chocolate chips and ½ cup butter in a medium saucepan over low heat. Stir until melted and smooth.

In a large bowl, combine 2 cups graham cracker crumbs, 1 cup mini marshmallows, and 1 cup nuts. Add peanut butter if using.

Pour the cooled chocolate mixture over the dry ingredients and fold until well coated.

Transfer the mixture into the prepared pan, pressing down firmly to pack the mixture.

Cover the pan and refrigerate for at least 2 hours until firm.

Melt 1 cup additional chocolate chips in a microwave-safe bowl.

Drizzle the melted chocolate over the bars once chilled and sprinkle with nuts or sprinkles if desired.

Cut into squares and serve. Store in an airtight container in the fridge.