Add water to veal, onion, and 2 teaspoons salt; simmer for 2 hours.
Skim, remove veal; slip meat from bones and chop fine; reserve 1 cup for meatballs.
Add remaining meat to broth.
Add flour stirred to a smooth paste with milk.
Season to taste with salt, pepper, and nutmeg.
Bring to a boil and serve at once over meatballs.