01 - Line an 8x8-inch baking pan with parchment paper, allowing overhang on opposite sides for easy removal later.
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 fully incorporated.
04 - Let the mixture cool for 2–3 minutes, then gently fold in 1 cup of Lucky Charms marshmallows until evenly distributed.
05 - Pour the fudge mixture into the prepared pan, using a spatula to spread it into an even layer.
06 - Sprinkle the remaining ½ cup of marshmallows evenly over the surface, pressing gently to adhere.
07 - Refrigerate for at least 2 hours or until completely firm and set throughout.
08 - Lift the fudge from the pan using the parchment overhang. Cut into 16 equal squares with a sharp knife.