01 - Line an 8x8-inch baking pan with parchment paper, leaving overhang on opposite sides for easy removal.
02 - In a medium saucepan over low heat, combine white chocolate chips, sweetened condensed milk, and butter. Stir constantly until completely smooth and melted.
03 - Remove from heat and stir in vanilla extract and pinch of salt until well incorporated.
04 - Let mixture cool for 2-3 minutes, then gently fold in 1 cup of Lucky Charms marshmallows until evenly distributed.
05 - Pour fudge mixture into prepared pan and spread evenly with a spatula.
06 - Sprinkle remaining ½ cup of marshmallows evenly over the surface, gently pressing to adhere.
07 - Refrigerate for at least 2 hours or until completely firm.
08 - Lift fudge from pan using parchment overhang and cut into 16 squares.