01 - Line an 8x8-inch baking pan with parchment paper, allowing overhang on sides for easy removal.
02 - Combine white chocolate chips, sweetened condensed milk, and butter in a medium saucepan over low heat. Stir continuously until completely smooth and melted.
03 - Remove from heat and stir in vanilla extract and salt until 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 into prepared pan, spreading evenly with a spatula to create a smooth surface.
06 - Sprinkle remaining ½ cup marshmallows over the top, pressing gently to adhere.
07 - Refrigerate for at least 2 hours or until completely firm.
08 - Lift fudge from pan using parchment overhang. Cut into 16 squares for serving.