01 - Line an 8x8-inch baking pan with parchment paper, allowing the sides to overhang for easy removal.
02 - In a medium saucepan over low heat, combine the white chocolate chips, sweetened condensed milk, and butter. Stir constantly until the chocolate is melted and the mixture is smooth.
03 - Remove from heat and quickly stir in the peppermint extract.
04 - Pour about three-quarters of the mixture into the prepared pan and spread evenly with a spatula.
05 - To the remaining mixture, add a few drops of red gel food coloring and stir until evenly colored.
06 - Drop spoonfuls of the red mixture over the white layer. Use a knife or skewer to gently swirl the two colors together to create a marbled effect.
07 - Sprinkle crushed peppermint candies evenly over the surface, gently pressing them in.
08 - Refrigerate for at least 2 hours, or until fully set.
09 - Lift the fudge from the pan using the parchment paper. Cut into squares and serve.