Heat a medium saucepan over medium heat. Combine in a medium saucepan over medium heat the butter, both types of chocolate chips, and sweetened condensed milk. Stir frequently until the chips and butter are melted and blended together. 

Remove the saucepan from the heat and add the vanilla extract and salt and stir to combine. Allow to sit for a few minutes so the mixture isn't so hot that it melts the marshmallows we'll be adding. Gently stir in the marshmallows and peanuts to the mixture, 

Pour the fudge mixture into an 8 x 8 prepared dish. 

I like to use silicone for the easy removal, but you can use a glass dish that’s been prepared with parchment paper, foil, or wax paper.

Smooth out the fudge to be equally distributed and then top with the handful of marshmallows and peanuts that were set aside. 

Allow the fudge to chill in the refrigerator until you are ready to cut and serve. Store any remaining fudge in an airtight container in the refrigerator for up to a week.