|  | 1 lb 2 oz (500 g) green asparagus | 
                      
                      
                      
                        
                          |  | 9 oz (400 g) smoked or fresh trout, cut in small pieces | 
                      
                      
                      
                        
                          |  | 3 tablespoons butter (for béchamel sauce) | 
                      
                      
                      
                        
                          |  | 3 tablespoons flour (for béchamel sauce) | 
                      
                      
                      
                        
                          |  | 2 ½ cups evaporated milk (for béchamel sauce) | 
                      
                      
                      
                        
                          |  | 1 cup cooking liquid from asparagus | 
                      
                      
                      
                        
                          |  | Instant (no-boil) lasagne | 
                      
                      
                      
                        
                          |  | ¾ cup grated parmesan cheese | 
                      
                      
                      
                        
                          |  | ½ cup shredded mozzarella cheese |