Line a large baking tray with parchment paper, and set aside.
Add the white chocolate to a microwave-safe bowl, and heat in 20 second intervals, stirring after each one, until melted and smooth. Stir in the peppermint extract, and food colouring. Set aside.
Melt the dark chocolate in the same way you melted the white chocolate. Pour onto the prepared baking tray, and spread out into a large rectangle.
Drizzle lines of the mint white chocolate on top (use a much or as little as you want of the mixture), and use a toothpick to swirl the two mixtures together. Sprinkle on your favourite mint chocolate candy (I used Quality Street's Mint Matchmakers).
Allow the chocolate to set at room temperature, or in the fridge. Once set, break into pieces, and enjoy!
Notes
Bark can be stored in an airtight container at room temperature or in the fridge for up to 3 weeks. It also freezes well for up to 2 months. Thaw overnight in the fridge before serving.