Line an 8x8 inch baking dish with parchment or wax paper. Set aside.
Add the chocolate chips, butter, and sweetened condensed milk.
Heat on 30 second increments, stirring well in between, until melted.
Add the hot chocolate mix and vanilla, and stir well to combine.
Fold in half of the miniature marshmallows.
Pour the fudge mixture into the baking dish, and smooth out evenly.
Top with remaining marshmallows, pressing the marshmallows gently into the fudge.
Chill in the refrigerator for 4 hours, or over night.
Cut into squares and enjoy.