Begin by lining a baking sheet with parchment paper. This will ensure that your Rocky Road Chocolate Bark doesn’t stick and makes for easy cleanup.
Using a double boiler, fill the bottom pot with water and bring it to a gentle simmer. Place the finely chopped chocolate in the top pot and stir occasionally until melted and smooth. Alternatively, heat the chocolate in a microwave in 30-second intervals, stirring in between until fully melted.
Once the chocolate is melted, remove it from heat and quickly stir in the miniature marshmallows and chopped walnuts. Make sure everything is evenly coated with chocolate.
Pour the chocolate mixture onto the prepared baking sheet. Use a spatula to spread it into an even layer, about ¼-inch thick.
Place the baking sheet in the refrigerator for about 30 minutes, or until the chocolate has set completely.
Once the chocolate has set, remove it from the refrigerator. Break the bark into pieces of your desired size. Serve immediately, or store it for later!