Prepare your pan: Line an 8x8-inch square baking dish with parchment paper, leaving some overhang on the sides.
Melt the chocolate: In a microwave-safe bowl or double boiler, melt the chocolate chips and butter together until smooth and glossy. Stir in the vanilla extract.
Let the chocolate cool slightly: Set the melted chocolate aside for 5 minutes so it’s warm but not hot—this prevents the marshmallows from melting.
Mix in the goodies: Gently fold in the mini marshmallows, chopped nuts, and graham cracker crumbs (or cereal). Stir until everything is evenly coated in chocolate.
Spread the mixture into the pan: Press the rocky road mixture into the prepared pan, spreading it out evenly. Sprinkle with extra nuts, chocolate chips, or sea salt if using.
Chill until set: Refrigerate the bars for at least 2 hours, or until they are firm and easy to slice.
Cut and serve: Lift the bars out of the pan using the parchment paper. Use a sharp knife to cut into 16 squares.
Store leftovers: Keep extras in an airtight container in the fridge for up to 1 week or freeze for up to 2 months.