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              Fry the onion in a frying pan with heated vegetable oil. Cut the champignons into quarters or thin slices, add to the onion and fry over medium heat, stirring constantly.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              After 10 minutes, salt the mushrooms and onions and continue to fry over moderate heat for another 10 minutes until cooked and moisture has evaporated.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              Transfer the mushroom and onion mixture to the ramekins, leaving 2-3cm at the edges for the sauce and cheese.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              Prepare the sauce: fry the flour in a dry frying pan for 3-4 minutes, stirring constantly. When the flour turns light brown, add sour cream to it and mix well so that there are no lumps.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              Pour warm filtered water into the pan and stir the sour cream mixture until smooth, bringing it to a boil over low heat.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              Pour the hot sour cream sauce over the mushroom and onion mixture and sprinkle each serving with cheese.
              
              
 
              
      
     
              
              
               
              
                  
                   
                   
               
              Place the filled molds into the preheated oven and bake for 15 minutes.