In a skillet, heat the olive oil over medium heat. Add the sliced onions and a pinch of salt, stirring occasionally for about 20-25 minutes until they are golden brown and caramelized.

In a mixing bowl, combine the ground meat, breadcrumbs, salt, and pepper. Form small meatballs, about 1 inch in diameter.

In a baking dish, layer half of the browned onions on the bottom. Place the meatballs on top, then pour the beef broth evenly over the mixture. Top with the remaining onions.

Sprinkle the shredded cheese generously over the top of the casserole.

Preheat your oven to 350°F (175°C), then bake the casserole for about 30-35 minutes, or until the meatballs are cooked through and the cheese is bubbly and golden.

Let it cool for a few minutes before serving. Serve generous portions on plates.