Gather all ingredients and line an 8x8-inch baking pan with parchment paper.

In a double boiler over medium heat, combine white chocolate chips and sweetened condensed milk. Stir until smooth, about 5-7 minutes.

Let the melted mixture cool slightly, then stir in peppermint extract.

Pour the mixture into the prepared pan. Melt the semi-sweet chocolate chips in the double boiler and drop spoonfuls on top, swirling for a marbled effect.

Sprinkle crushed peppermint candies on top, pressing them down lightly. Add red food coloring if desired and swirl again.

Chill in the refrigerator for at least two hours, then remove and slice into squares.