Line an 8x8 baking dish with parchment paper and set aside. In a double boiler, add the 1 1/2 cups of milk chocolate chips, 1 1/2 cups of semi-sweet chocolate chips, sweetened condensed milk, butter, and hot chocolate mix. Stir constantly over medium heat until smooth and melted.
Add 2 cups of the marshmallows and stir until completely melted and combined. Remove from the heat. Add in the vanilla and stir once more. Pour and scrape the fudge into the lined baking dish.
Sprinkle the remaining 2 cups of marshmallows on top of the fudge and lightly tap them into the fudge. Sprinkle the crushed peppermints all over the top of the marshmallows. Refrigerate for 3 hours.
Melt the 1/2 cup of semi-sweet chocolate in a microwave-safe bowl. Add the melted chocolate to a small zip-lock bag and set aside. Take the fudge out of the fridge and lift the parchment paper to remove it. Cut the fudge into 12 squares. Cut the tip off the ziplock bag and begin drizzling chocolate over the top of the fudge.
Place in the fridge for 5 minutes to let the chocolate harden. Serve and enjoy!