For dressing, in a blender or food processor bowl combine sour cream, grapefruit juice, honey, curry powder, cardamom, cinnamon, and pepper. Cover and blend or process until combined. With blender or processor running, slowly add salad oil in a steady stream until mixture is thickened. Cover and chill until ready to serve. Dressing can be prepared up to 3 days ahead of time.
Before serving, stir dressing to combine. Sprinkle with additional freshly ground pepper. Serve dressing with mesclun. Makes 12 servings.