4 (3 ounce) bars bittersweet chocolate
1 2/3 cups heavy cream
1/4 cup unsalted butter, softened (optional)
2 tablespoons Cognac (optional)
Break chocolate into pieces and process in food processor until very fine. Heat cream to the boiling point and, with the motor running, pour it through the feed tube in a steady stream. Process a few seconds until smooth. Transfer to a bowl and cool completely.
Gently stir in butter and/or Cognac. Allow to cool for several hours until of frosting consistency. If using butter, whisk for a few seconds to aerate. The color will lighten. To use Ganache as sauce, reheat until pourable if made ahead, using a double boiler or a microwave on low power, stirring every 15 seconds.
Makes 2 3/4 to 3 cups.