Chocolate melts best at temperatures between 104° and 113° F (40° and 45° C). Never melt chocolate directly over a heat source. Use an indirect heat source like a hot water bath so the chocolate reaches a temperature of 104° to 113° F (40° to 45° C). This is the perfect temperature to begin tempering.
Tempering is important because it determines the final gloss, hardness, and contraction of the chocolate. When you melt chocolate, the molecules of fat separate. In order to put them back together, you temper it. There are a variety of ways to do it.
One of the easiest ways to temper it is to place it in the microwave for 30 seconds at a time on high power until the chocolate is melted. Be very careful not to overheat it. Be careful; the chocolate will not look like it has melted because it retains its shape. The chocolate should be only slightly warmer than your bottom lip. You may still see lumps in it but, don't worry; the residual heat of the chocolate will melt them. You can also use an immersion blender to break up the lumps and start the recrystallization process. Usually, the chocolate begins to set (recrystalize) along the side of the bowl. As it begins to crystallize, mix those crystals into the melted chocolate and they will begin the recrystallization process. Jacque Torres likes to use glass bowl because it retains the heat and keeps the chocolate tempered a long time.
Another way to temper chocolate is called seeding. In this method, tempering is achieved by adding small pieces of unmelted chocolate to melted chocolate. The amount of unmelted chocolate to be added depends on the temperature of the melted chocolate but is usually one fourth of the total amount. Torres usually uses an immersion blender to mix the two together.
A simple method of checking tempering is to apply a small quantity of chocolate to a piece of paper or to the point of a knife. If the chocolate has been correctly tempered it will harden evenly and show a good gloss within five minutes.
Recipe courtesy of Dessert Circus, Extraordinary Desserts You Can Make At Home by Jacques Torres.