Wrap bananas in plastic wrap and freeze overnight.  Remove from freezer, break into 4 or 5 pieces and let stand at room temperature for about 10 minutes to slightly soften for the processor.    Blend the bananas in a processor or blender until creamy.  Add the Raspberry (or other flavor) sherbet and blend briefly.  This can be served immediately, or stored in the freezer.  Serves 4.