Chop bittersweet chocolate and in a double boiler or small metal bowl set over a saucepan of barely simmering water heat until melted. With a metal spatula spread melted chocolate onto a baking sheet (not non-stick) as thinly and evenly as possible. Cool chocolate until firm to the touch but not hard. (Alternatively, chill melted chocolate on sheet; if it becomes too hard let it soften slightly at room temperature.) With a pastry scraper or metal spatula held at an angle scrape chocolate slowly from sheet, letting it curl. Carefully transfer curls as formed to a plate lined with waxed paper. Make more curls with milk chocolate in same manner. Chocolate curls may be made 1 day ahead and chilled, loosely covered.
