Line a baking sheet with aluminum foil. Coarsely chop or grate:
     1 pound (1/2 pound for clusters) bittersweet or semisweet chocolate
Set aside two ounces of the chocolate and place the rest in the top of a double boiler or in a bowl set over, but not in, a pot of gently simmering water. Melt the chocolate slowly, stirring, until its temperature reaches 105° to 115°F. If you do not stir constantly at temperatures over 100°F, the cocoa butter will separate out. Transfer the chocolate to another bowl and cool to 100°F. Add the reserved chocolate and stir until the temperature cools to a maximum of 86°F for milk and white chocolates and 90°F for dark or bittersweet chocolate.
Stir in:
    2 cups finely chopped dried, candied, or crystallized fruit, candied ginger, and/or nuts
Stir to coat the fruit and nuts thoroughly.
For bark, spread the mixture about 1/4 inch thick on the lined baking sheet. Tap the pan on the work surface to release any air bubbles.
For clusters, use a tablespoon to drop the chocolate mixture onto the baking sheet.
Refrigerate the bark or clusters until firm, about 15 minutes. Then let stand in a cool place for 30 minutes to 1 hour to set completely.
To break the bark, hold the chocolate with the foil to avoid getting fingerprints on it, and break it into bite-sized, irregular shapes. If the bark is too hard to break with your hands, place a sheet of foil on top and hit it with a wooden spoon.
Store in an airtight container in the refrigerator for up to three weeks.