Boil the eggs for 10 min. with a pinch of salt. Peel them.
Flatten each meatball thinly. Put 1 whole boiled egg in the middle of each and wrap the meatball around it. Dip your hands in the water + vinegar to make this process easier. Shape the meatballs well.
Put them in an oven dish, covered with baking paper. Smear them with the lightly beaten yolk.
Bake in a 392°F (200 °C) oven until ready.