01 - Line an 8x8-inch baking pan with parchment paper, allowing the sides to overhang for easy removal of the fudge later.
02 - Combine white chocolate chips, sweetened condensed milk, and butter in a medium saucepan over low heat. Stir continuously until chocolate is completely melted and mixture achieves a smooth, glossy consistency.
03 - Remove saucepan from heat and immediately stir in peppermint extract until evenly distributed throughout the mixture.
04 - Pour approximately three-quarters of the fudge mixture into the prepared pan. Use a spatula to spread it into an even layer covering the bottom of the pan.
05 - Add several drops of red gel food coloring to the remaining fudge mixture in the saucepan. Stir thoroughly until the color is uniform throughout.
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 completely blending them.
07 - Sprinkle crushed peppermint candies evenly across the surface of the swirled fudge. Gently press the candy pieces into the surface to ensure they adhere properly.
08 - Refrigerate the pan for a minimum of 2 hours, or until the fudge is completely firm and set throughout.
09 - Use the parchment paper overhang to lift the fudge from the pan. Cut into small squares and serve immediately or store in an airtight container.