Before you start any melting, line your 8x8 pan with foil or parchment paper, leaving a bit of overhang on the sides. This little step makes lifting the finished fudge out so much easier later, and it saves you from scraping a sticky pan.
Open your can of sweetened condensed milk and give it a really good stir before measuring out your ½ cup. Some brands separate a bit inside the can, and stirring first helps your fudge set properly later on.
In a saucepan over low heat, combine your white chocolate chips and sweetened condensed milk. Stir often so nothing scorches on the bottom, and keep going until the mixture turns completely smooth and glossy.
Once your chocolate base is smooth, remove it from the heat and stir in the pumpkin puree, pumpkin pie spice, vanilla, and salt. Keep stirring until everything is fully combined and you get a consistent orange color throughout.
Pour the mixture into your prepared pan and smooth the top with your spatula. Refrigerate for at least 3 hours, or until the fudge feels firm to the touch and holds its shape when you press it lightly.
Once fully set, lift the fudge out using the foil overhang and place it on a cutting board. Slice into small squares with a sharp knife, wiping the blade clean between cuts for the neatest edges.