01 - Line an 8x8-inch baking pan with parchment paper, allowing the sides to overhang for easy removal later.
02 - In a medium saucepan over low heat, combine the white chocolate chips, sweetened condensed milk, and butter. Stir constantly until the chocolate is completely melted and the mixture becomes smooth and creamy.
03 - Remove the saucepan from heat and immediately stir in the peppermint extract until well incorporated.
04 - Pour approximately three-quarters of the fudge mixture into the prepared pan. Use a spatula to spread it evenly across the bottom.
05 - Add a few drops of red gel food coloring to the remaining fudge mixture in the saucepan. Stir thoroughly until the color is evenly distributed.
06 - Drop spoonfuls of the red fudge mixture over the white layer in the pan. Use a knife or skewer to gently swirl the two colors together, creating a marbled pattern without over-mixing.
07 - Sprinkle the crushed peppermint candies evenly over the surface of the swirled fudge. Gently press the candies into the fudge to ensure they adhere properly.
08 - Refrigerate the fudge for at least 2 hours, or until completely firm and set throughout.
09 - Lift the fudge from the pan using the overhanging parchment paper. Cut into 25 equal-sized squares and serve immediately or store in an airtight container.