01 - Line an 8x8-inch baking pan with parchment paper, allowing the sides to overhang for easy removal later.
02 - Combine white chocolate chips, sweetened condensed milk, and butter in a medium saucepan over low heat. Stir constantly until completely melted and smooth.
03 - Remove from heat and stir in peppermint extract until well incorporated.
04 - Pour approximately three-quarters of the mixture into the prepared pan. Spread evenly using a spatula.
05 - Add red gel food coloring to the remaining mixture in the saucepan. Stir until uniformly colored.
06 - Drop spoonfuls of the red mixture over the white base layer. Use a knife or skewer to gently swirl and marble the colors together.
07 - Sprinkle crushed peppermint candies evenly over the surface, pressing gently to adhere.
08 - Refrigerate for at least 2 hours until completely firm and set.
09 - Lift the fudge from the pan using the parchment paper overhang. Cut into squares and serve.