Very bittersweet and glossy. Use to fill and frost any chocolate butter cake. Prepare this just before using.
Melt, stirring often, in the top of a double boiler or in a microwave on medium:
      10 ounces bittersweet chocolate or semisweet chocolate, coarsely chopped
Remove from the heat and stir in (do not beat) just until combined:
      1 cup sour cream
Use immediately; if the frosting becomes too stiff or loses its gloss at any time, set the pan in a larger pan of hot water for a few seconds and stir to soften. This keeps, refrigerated, for up to 1 week. Or freeze for up to 6 months. Soften before using.