Bark can be refrigerated in an airtight container up to one week.
Put chocolate in a small heatproof bowl set over a pan of simmering water, and stir until almost completely melted. Remove bowl from pan, and stir occasionally until chocolate registers 90 degrees on a candy thermometer. Pour onto a baking sheet, and spread evenly with an offset spatula.
Refrigerate chocolate until firm, about 20 minutes. Rub a bench scraper back and forth across surface to make shavings and splinters that resemble bark.