Line an 8X8 or 9X9 baking pan with parchment paper or foil. Then spray it with non-stick cooking spray.
Place the semi-sweet chocolate chips, half of the milk chocolate chips, butter, sweetened condensed milk and the hot chocolate mix in a large microwave safe bowl.
Microwave in 30 second intervals, stirring after each interval until all the ingredients are melted and smooth. Be careful not to over heat or the chocolate could burn.
Then stir in the vanilla extract and half of the miniature marshmallows.
Pour the mixture into the prepared pan and press the remaining marshmallows on top of the fudge. Gently press them down so that they sit into the top of the fudge.
Refrigerate until the fudge is set (4-6 hours).
Microwave the remaining milk chocolate chips in a small bowl by heating it in 30 second intervals. Drizzle this melted chocolate on top of the marshmallows on the fudge. Let this chocolate sit to harden (30-60 minutes).
Then carefully lift the parchment paper or foil out of the pan. Cut the fudge into pieces and enjoy!