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 glossy.
03 - Remove the saucepan from heat and quickly stir in the peppermint extract until evenly distributed throughout the mixture.
04 - Pour about 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 mixture in the saucepan. Stir thoroughly until the color is uniform and vibrant.
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 overmixing.
07 - Sprinkle the crushed peppermint candies evenly over the surface of the swirled fudge. Gently press them into the mixture to ensure they adhere.
08 - Refrigerate the pan for at least 2 hours, or until the fudge is completely firm and set throughout.
09 - Lift the fudge from the pan using the overhanging parchment paper. Cut into 25 equal squares and serve chilled or at room temperature.