To make decorative chocolate curls, wrap a medium-size chunk of semisweet chocolate in plastic wrap. Rub the wrapped chocolate between your hands for 1 or 2 minutes to warm it; the chocolate should not melt. For larger chunks, microwave on low for about 5 seconds. Unwrap the chocolate and, using a vegetable peeler, slowly and evenly scrape the edge of the chunk until curls form. If the chocolate is cold, the peeler will make ragged shavings rather than curls, so repeat warming the chocolate as necessary.