Prepare the Pan: Line an 8x8-inch baking dish with parchment paper, leaving some overhang on the sides for easy removal later.
Melt the Chocolate: In a medium saucepan over low heat, combine the semi-sweet chocolate chips and 1 cup of sweetened condensed milk. Stir constantly until fully melted and smooth. Remove from heat and stir in the vanilla extract.
Create the White Chocolate Layer: In another saucepan, repeat the same process with the white chocolate chips and the remaining sweetened condensed milk. Once melted, stir in the peppermint extract and 1/4 cup of crushed candy canes. If using, add a few drops of red and green food coloring to create a festive swirl effect.
Layer the Fudge: Pour the melted semi-sweet chocolate mixture into the prepared baking dish, smoothing it into an even layer. Next, carefully spoon dollops of the white chocolate mixture over the semi-sweet layer. Using a toothpick or knife, swirl the two layers together gently for a marbled effect.
Final Touch: Sprinkle the remaining crushed candy canes on top of the fudge, and a light sprinkle of sea salt for contrast.
Chill: Refrigerate the fudge for at least 2 hours, or until fully set.
Cut and Serve: Once set, use the parchment overhang to lift the fudge out of the pan. Cut into squares and serve.
Notes
Arrange the fudge squares on a festive platter and consider garnishing with a sprig of mint for a pop of color. Place small decorative bags or boxes of fudge as holiday gifts for friends and family.