Prep your pan: Line an 8x8 inch baking dish with parchment paper. Set aside.
Melt the chocolate: In a microwave-safe bowl, combine chocolate chips and butter. Microwave in 30-second intervals, stirring each time, until smooth. (Or melt over low heat in a saucepan.)
Mix-ins: Stir in mini marshmallows, chopped nuts, and crushed graham crackers (if using).
Assemble: Pour the mixture into your prepared dish. Spread evenly.
Chill: Refrigerate for at least 1 hour or until firm.
Cut & Serve: Once set, lift out using parchment, cut into squares, and enjoy