Step 1

Cut the chocolate into triangles when it has just turned matte but is not yet fully hardened. Luster dust is a fine, edible, iridescent powder that gives sweets a little extra finesse. It can be found at cake decorating shops or online. The chocolate decorations can be wrapped well and refrigerated for up to one week.

Step 2

Invert rimmed baking sheet and top with sheet of parchment paper. Tape parchment to sheet. Microwave chopped chocolate in bowl at 50 percent power, stirring every 30 seconds, until melted but not much warmer than body temperature (check by holding bowl in palm of your hand), 2 to 3 minutes. Add grated chocolate and stir until smooth, returning to microwave for no more than 5 seconds at a time to finish melting if necessary.

Step 3

Spread chocolate thinly and evenly over prepared parchment to form rough 8 by 12-inch rectangle. Refrigerate until surface of chocolate just turns matte, 1 to 2 minutes. Using tip of sharp knife, cut half of chocolate into tall, slim triangles. Refrigerate until fully hardened, about 10 minutes. Brush triangles with luster dust, if using. Break remaining chocolate into 1-inch shards. Refrigerate until needed.