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 the peppermint extract until well incorporated.
04 - Pour approximately three-quarters of the mixture into the prepared pan, spreading evenly with a spatula.
05 - Add several drops of red gel food coloring to the remaining mixture. Stir until uniformly colored.
06 - Drop spoonfuls of the red mixture over the white layer. Use a knife or skewer to gently swirl the colors together, creating a marbled pattern.
07 - Sprinkle crushed peppermint candies evenly across the surface, pressing gently to adhere.
08 - Refrigerate for at least 2 hours or until completely firm.
09 - Lift the fudge from the pan using the parchment paper overhang. Cut into squares and serve.