1. Line an 8×8 inch pan with parchment, leaving overhang on two sides for easy lifting.

2. In two microwave-safe bowls, add white chocolate chips to one and semi-sweet chips to the other.

3. Melt each bowl in 30-second intervals, stirring between bursts until smooth; or use a double boiler for gentle melting.

4. Stir half of the condensed milk into the white chocolate until glossy and smooth.

5. Stir the remaining half of the condensed milk into the semi-sweet chocolate until glossy and smooth.

6. Add peppermint extract to the white chocolate mixture and stir to combine.

7. Pour half of the semi-sweet mixture into the pan and spread evenly; spoon half of the white mixture on top. Repeat layering with the remaining mixtures.

8. Gently swirl a knife through the layers with large movements to create a marbled effect.

9. Sprinkle crushed peppermint candies evenly over the top. If desired, dot with red food coloring and lightly swirl for a candy-cane look.

10. Refrigerate for at least 4 hours, or until fully set and firm to the touch.

11. Lift the slab out using the parchment overhang. Slice into small squares and serve chilled.