Serves4
                    
                
                
                    
                        
                            - Active time:30 min
 
                        
                            - Start to finish:2 3/4 hr(includes chilling)
 
                        
                    
                
             
            
            
                
                
                
    
      
          
          
          
              
              
              
          
          
          
          
          
              
              
              June 2004
            
          
          
      
  
                
                
            
            
            
                There’s no need to trim the watercress; you can use every bit of it in this recipe.
            
            
            
            
            
                
                    
                    
                    
                        
                            For filling
                            
                            
                                
                                    
                                        - 
                                            1
                                            
                                            small boiling potato (1/4 lb), peeled and cut into 1/2-inch pieces
                                            
                                        
 
                                    
                                        - 
                                            1
                                            
                                            small onion, finely chopped
                                            
                                        
 
                                    
                                        - 
                                            2
                                            cups
                                            (16 fl oz) low-sodium chicken broth
                                            
                                        
 
                                    
                                        - 
                                            1
                                            cup
                                            heavy cream
                                            
                                        
 
                                    
                                        - 
                                            4
                                            cups
                                            coarsely chopped watercress (1 large bunch)
                                            
                                        
 
                                    
                                
                            
                         
                    
                 
            
            
            
            
            
            
            
            
                
                    
                    
                    
                        
                            
                                
                                
                                
                                    
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Simmer potato, onion, broth, and cream, uncovered, in a 3- to 4-quart heavy saucepan until vegetables are soft, about 10 minutes. Stir in watercress and cook mixture, uncovered, over moderately low heat 3 minutes more.
                                         
                                    
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Purée soup in 2 batches in a blender until very smooth, about 45 seconds per batch (use caution when blending hot liquids). Force soup through a fine-mesh sieve into a bowl, pressing hard on solids and then discarding them. Season with salt and pepper and let soup stand, uncovered, until cool, 45 minutes, then chill, covered, 1 1/2 hours.
                                         
                                    
                                
                             
                        
                    
                    Cooks’ notes: - Soup can be chilled quickly in a metal bowl set in a larger bowl of ice and cold water. Stir occasionally for 15 minutes, then remove from cold water and refrigerate, covered, until cold, about 30 minutes.
  - Soup can be chilled, covered, up to 2 days.