1. Line an 8-inch square pan with parchment paper, leaving overhang on the sides.

2. Add semisweet chocolate chips, half of the sweetened condensed milk, 1 tablespoon butter, and salt to a saucepan over low heat.

3. Stir until melted, smooth, and glossy, then remove from the heat and mix in peppermint extract and vanilla extract.

4. In a separate saucepan or microwave-safe bowl, melt white chocolate chips with the remaining sweetened condensed milk and 1 tablespoon butter until smooth.

5. Spread most of the chocolate mixture into the prepared pan.

6. Spoon the white chocolate mixture over the top in dollops, then add the remaining chocolate mixture in a few spots.

7. Use a knife or skewer to gently swirl the layers together without overmixing.

8. Sprinkle crushed candy canes over the top and press them in lightly.

9. Refrigerate for at least 3 hours, or until completely firm.

10. Lift the fudge from the pan and slice into small squares.