Using a serrated knife, finely chop the chocolate into 1/4-inch pieces. Don't be lazy here. Big chunks will not melt.
Traditional method: Place the chocolate in a medium heatproof bowl. Bring the cream to a boil in a small saucepan over medium heat. Boiling means the cream will actually rise up in the pan and threaten to boil over.
Immediately pour the boiling cream over the chopped chocolate. Tap the bowl on the counter to settle the chocolate into the cream, then let it sit for 1 minute. Using a rubber spatula, slowly stir in a circular motion, starting from the center of the bowl, and working out to the sides. Be careful not to add too much air to the ganache. Stir until all the chocolate is melted, about 2 minutes. It may look done after 1 minute of stirring, but keep going to be sure it's emulsified.
Food processor method: Place the chopped chocolate in a food processor fitted with the steel blade. Bring the cream to a boil in a small saucepan over medium heat (or bring to a boil in the microwave.)
Immediately pour the hot cream into the food processor, on top of the chocolate. Let sit for 1 minute, then pulse the machine 3 times. Scrape down the sides with a rubber spatula and pulse 3 more times, until all the chocolate is melted. This smooth, silky chocolate is now ganache. Transfer the ganache to a bowl.
Let the ganache sit at room temperature until it cools to 70 degrees F. In a 65 degree F room, this will take approximately 4 hours or 2 hours in the refrigerator. You can speed up the process by pouring the ganache out onto a clean baking sheet (thinner layers cool faster.) Once the ganache reaches 70 degrees F, it is ready to be used. At this point it can be covered and stored in the refrigerator for up to 2 weeks.
Recipe courtesy of Sherry Yard, The Secrets of Baking, Houghton Mifflin, 2003