Prep Pan:
Line an 8×8 or 9×9-inch square baking pan with parchment paper, leaving an overhang for easy removal. Lightly spray with cooking spray.

Melt Chocolate Layer:
In a double boiler (or microwave in 30-second intervals), melt the semi-sweet chocolate chips with half of the sweetened condensed milk. Stir until smooth. Pour into the prepared pan and spread evenly. Refrigerate for 10 minutes to set.

Make Peppermint Layer:
In another bowl, melt the white chocolate chips with the remaining sweetened condensed milk. Stir until smooth, then mix in peppermint extract and a few drops of red food coloring, if using.

Swirl & Top:
Pour the peppermint layer over the chocolate layer. Use a knife or toothpick to gently swirl the layers together for a marbled look. Sprinkle crushed peppermint candies on top and lightly press them in.

Chill & Serve:
Refrigerate for at least 4 hours or overnight until fully set. Use a warm knife for clean cuts and slice into 36 small squares. Serve or gift!