I made about 6 lbs of this yesterday, so figured I'd share.
2 lb dark chocolate, chopped finely
4 oz milk chocolate, chopped finely
To make fruit & nut bark: 4 cups of dry roasted nuts and dried fruits. For example, dried cherries and almonds, raisins and peanuts, cranberries and pecans, etc.
To make pretzel bark: 6 cups mini pretzels, "lightly broken up" but still in big chunks. Some other options to add in: peanut butter or butterscotch chips, toffee bits, nuts, etc.
If using nuts, toast them for full flavor. Heat the oven up to 350 degrees. Spread the nuts out on a baking sheet in a single layer. Turn the oven off, and put the nuts in for about 10 minutes, shaking the pan halfway through. Cool.
Line a cookie sheet with parchment paper and set aside.
To melt the chocolate: put 2/3 of the dark chocolate in a microwave safe bowl. Nuke on 30 second increments at 50% power, stirring at every stop. When the chocolate is mostly melted but not perfectly smooth, remove from microwave and add remaining 1/3 reserved chocolate. Stir until chocolate is melted and smooth.
Stir in add-in's of choice, and spread out on parchment lined cookie sheet.
Melt the milk chocolate using the above method. Scrape into a plastic baggie and push chocolate into one corner. Snip a small corner off the bag, and drizzle the milk chocolate on top of the chocolate bark. Sprinkle with holiday jimmies.
Let set firm (3-4 hours). Using a sharp serrated knife, cut into squares.