Traditional Flemish Waterzooi Recipe

Name: Traditional Flemish Waterzooi Recipe
Prep time: 30 min
Cook time: 20 min
Total time: 50 min
Cuisine: European
Ingredients: 10.5 oz./300 g. potatoes (peeled); 2 tbsp./30 g. butter; 1 stalk celery (finely sliced); 1 carrot (finely sliced); 1 onion (finely sliced); 1 leek (finely sliced); 7/8 cup/7 fl. oz./200 ml. fish stock; 5 oz./150 g. fillet plaice (skinless, cut into pieces); 5 oz./150 g. fillet haddock (skinless, cut into pieces); 3.5 oz./100 g. mussels (cleaned, see Tips below); 1 egg yolk; 2/5 cup/3.5 fl. oz./100 ml. cream; 3.5 oz./100 g. shrimp (peeled Hollandse garnalen [brown shrimp] or 10.5 oz./300 g. unpeeled shrimp); 1 tbsp. chives (finely chopped); Salt & freshly cracked pepper to taste; Pepper