1-Line an 8×8 baking dish with parchment: Line an 8×8 baking dish with parchment paper, leave a slight overhang to help in lifting the fudge out of the pan (You can use small binder clips to fasten the top edge of the parchment paper to the baking dish. That will help ensure the parchment paper does not fold over on top of the fudge as they firm up). Lightly spray the parchment paper with nonstick cooking spray.
2-Add the semi sweet and milk chocolate: Add the semi sweet and milk chocolate chips, sweetened condensed milk, hot chocolate mix and sliced butter pats to a medium size microwave safe bowl. Heat at full power for 1 minute, stir well and continue to microwave in 45 second increments until the chocolate is melted and completely smooth. (This should take about 2 ½ to 3 minutes)
3-Stir in the vanilla until completely incorporated: Stir in the vanilla until completely incorporated.
4-Stir in 2 cups of the miniature: Stir in 2 cups of the miniature marshmallows until well incorporated, reserving the remaining 2 cups for the topping. Microwave for 20 to 30 seconds, and stir 2 to 3 times.
5-Pour the fudge into the prepared baking: Pour the fudge into the prepared baking dish. Use an offset spatula to evenly spread the fudge.
6-Sprinkle the remaining miniature marshmallows over the: Sprinkle the remaining miniature marshmallows over the surface of the fudge. Gently press the miniature marshmallows down to ensure they adhere to the surface of the fudge.
7-Cover the top of the baking dish: Cover the top of the baking dish with plastic wrap and chill in the refrigerator for 2 hours or until firmly set.
8-Once the fudge is set, remove the: Once the fudge is set, remove the binder clips and use the overhang of parchment paper to lift the fudge out of the pan onto a cutting board.
9-In a microwave safe bowl heat the: In a microwave safe bowl heat the chocolate chips and vegetable oil for 30 seconds, and stir until melted and smooth. Drizzle the tops of the miniature marshmallows with the chocolate.
10-Allow the chocolate to dry before using: Allow the chocolate to dry before using a sharp kitchen knife to cut 5 slices x 5 slices. Keep refrigerated until ready to serve.