2. Scoop up some of the chilled chocolate mixture with a teaspoon and roll between your palms to make 3/4-inch balls (they don't have to be perfectly round). Work quickly so the chocolate doesn't melt in your hands. Transfer the balls to a waxed paper-lined baking sheet, setting them 1/2-inch apart. Wipe your hands periodically with paper towels to remove any chocolate left behind from rolling. If the truffle mixture becomes too soft to roll, return it to the refrigerator briefly to firm up before continuing.
3. Lightly cover the balls with plastic wrap and return to the refrigerator until cool and firm. Place the cocoa powder in a pie plate or other flat-bottomed dish with sides, and roll the truffles in the cocoa powder a few at a time, until coated. Store the truffles in a waxed paper-lined tin in the refrigerator until ready to serve.
Adam Rapoport, editor in chief of Bon Appetit magazine and the website www.bonappetit.com, knows his way around a grill. He has edited an entire book on the subject: The Grilling Book: The Definitive Guide from Bon Appetit.