Add the minced meat, the crumbled sausage, the lightly squeezed bread, the egg, the Parmesan and a pinch of salt, and mix.
With slightly moistened hands, take a little mixture at a time, flatten it in your hands, put a small piece of cheese in the center and close to form a meatball.
Continue like this with all the other meatballs, then pass them in the breadcrumbs, making it adhere evenly.
Meanwhile, brown your meatballs in another non-stick pan with a little oil, turning them to brown them evenly, then quickly pass them back into the pan with the onions, blending with a little broth, just long enough to flavor.
The sausage and chestnut meatballs are ready, serve them immediately.