To prepare ganache: Line an 8-inch-square pan with foil, letting it overhang two opposing sides slightly. Lightly coat with cooking spray.
Combine cream, orange zest, orange juice, sugar and orange liqueur (or vanilla) in a 2-cup glass measure or microwave-safe bowl. Microwave on High until steaming, about 1 minute; watch to avoid boiling over. (Alternatively, combine in a small saucepan and heat over medium-low heat until just steaming.) Stir until the sugar dissolves. Set aside for 10 minutes.
Place 8 ounces chocolate in a medium microwave-safe bowl. (Alternatively, see "No Microwave?" below.) Microwave on High for 1 minute. Microwave on Medium, stirring every 20 seconds, until mostly melted. Set aside.
Return the cream mixture to the microwave (or stove) and microwave on High (or heat on medium-low) until steaming again. Strain the mixture through a fine sieve set over the chocolate, pressing down to force through as much liquid as possible; don't stir the chocolate. Let stand without stirring for 2 minutes. Using a clean, dry spoon, slowly stir the cream mixture into the chocolate until smoothly incorporated; at first the ganache will look separated but it will gradually come together after several minutes of stirring. (If any unmelted chocolate remains, return the bowl to the microwave and microwave on Medium for 30 seconds. Stir until completely smooth.) Pour into the prepared pan. Rap it several times to even the surface. Set aside until cooled completely, 3 to 4 hours. Cover and refrigerate until cold and firm, at least 6 hours and up to 2 days. (If the ganache is not very firm when pressed, place it in the freezer for up to 1 hour. If rock-hard, remove from the refrigerator and let warm up for several
To shape truffles: Line a large baking sheet with foil. Transfer the ganache to a cutting board. Peel off the foil. Using a large sharp knife, cut the slab into quarters. Wrap each quarter separately in foil and freeze until firm, about 30 minutes. Working with one quarter at a time, cut into 12 equal pieces (thirds lengthwise and fourths crosswise). Shape each piece into a rough round, then roll it into a ball between your palms; they don't have to be perfect. Avoid overhandling the balls and wipe off chocolate buildup on your hands with paper towels. Place the balls on the prepared pan. Repeat with the remaining quarters. Cover with plastic wrap and freeze until thoroughly chilled, about 1 hour.
To coat truffles: Put cocoa in a small deep bowl. Place 8 ounces chocolate in another small microwave-safe bowl and microwave on High for 1 minute; stir well. Continue microwaving on Medium, stirring every 20 seconds, until mostly melted. Stir until the remaining chocolate melts completely.
Line another large baking sheet with foil. Remove a dozen balls from the freezer. Working with one ball at a time, quickly submerge it into the chocolate, turning with a fork to coat it completely. Lift the ball out with the fork, tapping it several times against the side of the bowl to remove excess chocolate. (You only want a thin layer of chocolate covering the ball.) Immediately toss the truffle into the cocoa, swirling the bowl until the truffle is evenly coated. Transfer to the prepared pan. Repeat with the remaining balls of chocolate until they are all coated, stirring the chocolate occasionally. If the chocolate cools and hardens, microwave it on Medium for 10-15 seconds, then stir before continuing. Refrigerate the truffles until well chilled.
No Microwave? Melt chocolate in a double boiler instead: Place chopped chocolate in the top of a double boiler over hot, but not boiling water. Gently stir until the chocolate is almost melted. Remove from the heat and stir until it melts completely. Ingredient note: Superfine sugar is an instantly dissolving sugar and is used in this recipe to guarantee a smooth, silky ganache filling. It is commonly available in the baking section of most supermarkets, but if you can't find it, simply process regular granulated sugar in a food processor until ground very fine.