Line square baking dish (8x8" or 9x9") with aluminum foil. Spray the foil with cooking spray. 

Add butter to a medium saucepan over medium heat. Allow the butter to mostly melt, and then add in the sweetened condensed milk and white chocolate chips. Stir until chips are melted - about 2 minutes. Add in mini marshmallows, stir occasionally until they dissolve into the mixture - about another 2 minutes - and then remove from heat. Stir in cloves, cranberries, and pistachios.

Pour the mixture into prepared pan, ensuring you get it to spread as evenly as you can across the pan. (It's not going to be very runny, so don't worry about trying to fit every nook and cranny. Gravity will eventually help it settle.) 

Immediately sprinkle chopped nuts on top.

Allow to cool a bit on the counter before transferring to the fridge to set overnight. (No need to cover with plastic wrap.) 

Remove pan from fridge, lift fudge out with foil, and then use a sharp knife to slice fudge into about 32 smaller pieces. You can make fewer cuts than this to produce larger pieces of fudge, but because this is such a decadent and sweet treat, I like to make smaller pieces. 

Store in an airtight container at room temperature for several days. It'll stay moist & delicious for quite a while!