Soak the bread rolls in some water. Once soft, squeeze out all the liquid with the help of a colander or cheesecloth. This is important as you do not want your meatballs to become too soggy.
Chop the onion finely. Heat the butter in a frying pan and fry the onions until translucent.
In a large bowl, add the mince, bread pulp, egg, breadcrumbs, lemon peel, fried onions and, if you want anchovy or anchovy paste. Combine to a smooth mass. Season with salt and pepper. From there form some meatballs. Mine were about 7 cm in diameter. Place them on a plate, cover them and place them in the fridge. (This will help them to harden a bit).
Now let’s start making the broth/stock. Place all ingredients in a large pot (at least 5 liter). Bring the broth/stock to a boil and then reduce the heat so it just simmers. Add the meatballs to the simmering water. (The water should simmer not boil wildly!). Leave to slowly cook for 15-20 minutes. Always check that the largest meatball is cooked through before removing all the meatballs from the broth. Remove all the meatballs with a slotted spoon and place on a plate. Measure off 350 ml of the broth and set aside.
To make the sauce, melt the butter in the saucepan. Add flour and mix until it forms a smooth paste. Slowly pour in the broth. Bring to boil for about 5 minutes. Remove the pot from the heat. Now add the drained capers and cream. Add lemon juice and season with some sugar and salt and pepper to taste. Mix in the egg yolk to thicken the sauce.
Pour the sauce over the meatballs. Serve with chopped parsley.