Preheat the oven to 350 degrees F.
Place the nuts in a large mixing bowl. Add the corn syrup. Stir until evenly coated. Add the granulated sugar. Stir until coated. Place the nuts on a baking sheet. Roast in the oven for 15 to 20 minutes. Remove from the oven. Use a wooden spoon to transfer the nuts onto a parchment paper-covered baking sheet. Do not touch the nuts as they are extremely hot. The nuts need to be cooled before the chocolate coating is applied. The coating process will be easier if you place the nuts in the freezer because the cold nuts will help the chocolate to temper. You can also let the nuts cool completely at room temperature. When completely cooled, break apart any nut clusters that may have formed.
Place the cooled nuts in the coating pan or in a large mixing bowl. If you are using the coating pan, turn the stand mixer on low speed, and let it continue to turn throughout all of the following steps. Slowly add one third of the tempered chocolate, one ladle at a time. If you are using the mixing bowl, fold the nuts into the chocolate until they are thoroughly coated and the chocolate has set. If you do not fold immediately, the chocolate will set and the nuts will stick together. Add another third of the chocolate and fold thoroughly until set. Add the remaining third and fold thoroughly being sure all the nuts are well coated. Separate any clusters of nuts that may have formed. If you serve the nuts as they are, let the chocolate set completely. If you decide to move on to the next step, and coat the nuts in confectioners' sugar or cocoa powder do not wait for the chocolate to set completely.
Add the powdered sugar or cocoa powder, if using, and stir until all of the nuts are well coated. If you'd like to coat half of the nuts in confectioners' sugar and the other half in cocoa powder, start with the confectioners' sugar. Before serving, place the nuts in a sieve to remove any excess sugar or cocoa powder. The nuts will keep at room temperature in an airtight container for up to 2 weeks.
Cooks NoteTo temper the chocolate so that it maintains a nice gloss or sheen when melted and doesn't harden leaving a white film (fat separation), chop the chocolate into small pieces and place in a microwave-safe bowl or measuring cup. Microwave the chocolate for 30 seconds on high power, or until most of the chocolate is melted. The temperature should read between 88 and 90 degrees F for dark chocolate and 86 to 88 degrees F for milk chocolate and white chocolate. Do not overheat. Stir the chocolate until the remaining lumps melt and the consistency is smooth (the residual heat will melt the lumps.)