Prepare a double boiler with 2 inches of water in the bottom saucepan. Bring to a simmer.
Add the cacao butter to the top bowl and allow it to melt completely. Whisk in the coconut oil until combined well. Turn off the flame.
Sift in the powdered sugar and keep whisking vigorously until combined and smooth. Add the vanilla extract and whisk again.
Carefully transfer 1/3 of the white chocolate mixture to a cup and place in the freezer to thicken up for 10 minutes.
Meanwhile sift the cacao powder in the remaining white chocolate mix and whisk well until smooth. Add more cacao powder to your liking.
Line a small shallow rimmed baking sheet with parchment paper. Pour the dark chocolate and spread evenly. Place the tray in the freezer for 10 minutes to set.
Remove the dark chocolate from the freezer and drizzle it over the top with the reserved white chocolate. Use a spatula to help spread it across the top.
Sprinkle the top with the cranberries, mint leaves and cacao nibs. Place back into the freezer for about 45 minutes to 1 hour until fully solid.
Use a sharp knife to cut the bark into chunks, place in a sealed glass container and keep in the freezer until needed. You could also store it in the refrigerator for a few days.