Start by cutting the sliced bread into small cubes.
Transfer them to a bowl, add the milk and let them soak for 15 minutes.
After this indicated time, mash them well and set aside.
In another bowl, add the ground beef, the moistened and mashed bread, the chopped chives, the grated mozzarella cheese and the eggs.
Season with the salt, the black pepper and the nutmeg, mix all the ingredients very well until combined.
After that, split the mixture into 2 equal portions, get one of the portions and round it just like shown in the video, then set aside. Repeat the same process with the other portion.
Now, in a nonstick baking sheet, add one drizzle of oil and spread well.
Coarsely chop the onion and spread the pieces all over the baking sheet.
Cover them with the meatballs.
Sprinkle sweet paprika all over the meatballs, to taste.
Take to a preheated oven at 180°C (356°F) and bake for 1 hour.
Serve.