1. Line an 8×8-inch pan with parchment paper and lightly butter the sides

2. In a saucepan over low heat, combine white chocolate chips, sweetened condensed milk, butter and salt; stir until smooth then remove from heat and mix in vanilla and half the peppermint extract

3. In a separate bowl or double boiler, melt dark chocolate chips with the remaining peppermint extract until glossy

4. Pour half of the white chocolate mixture into the pan and smooth into an even layer

5. Spoon dollops of the dark chocolate mixture and remaining white chocolate over it, then use a skewer or knife to create marble swirls

6. Sprinkle crushed peppermint candies on top and refrigerate for at least 3 hours until firm

7. Lift the fudge from the pan using parchment edges and cut into squares with a warm, dry knife