Line an 8x8 inch square pan with foil or parchment paper and spray with cooking spray.

In a double boiler, add 1 1/2 cups semi-sweet chocolate chips, 1 1/2 cups milk chocolate chips, butter, sweetened condensed milk, and hot chocolate mix. Stir to combine.

Continue to stir over medium heat until the chips are completely melted.

Add 2 cups of marshmallows and stir for 1 minute. Remove from the heat.

Add in the vanilla and stir until incorporated.

Pour the fudge into the prepared pan and gently press the remaining marshmallows into the top of the fudge.

Refrigerate for 4 hours.

Remove the fudge from the pan and cut it into squares.

Heat the remaining 1/2 cup of chocolate in the microwave in 30-second intervals, stirring after each interval until completely melted.

Drizzle over the fudge and let cool completely.