Peel the outer skin from the onions and slice off about 1/2 inch from the top and a thin layer from the bottom for stability.

Bring a large pot of salted water to a boil and parboil the onions for 10-15 minutes until slightly tender.

Remove the onions with a slotted spoon and cool them in ice water or under cold water, then drain.

Hollow out the onions, leaving about 2-3 outer layers intact, and chop the scooped-out centers.

In a skillet, heat 1 tablespoon of olive oil and sauté the chopped onion for 5-7 minutes until softened, then add minced garlic and cook for 1 minute.

Add the ground meat to the skillet and brown over medium-high heat, then drain excess fat.

Stir in tomato paste, oregano, thyme, salt, black pepper, and red pepper flakes, cooking for 2-3 minutes.

Transfer the meat mixture to a mixing bowl, add cooked rice or breadcrumbs, Parmesan cheese, parsley, and beaten egg, mix gently until combined.

Preheat the oven to 375°F (190°C) and lightly grease a baking dish with olive oil or butter.

Fill the hollowed onions with the meat and rice filling, packing it gently and placing them upright in the baking dish.

Pour broth around the base of the onions in the baking dish and cover tightly with aluminum foil.

Bake covered for 45-60 minutes until fork-tender, then uncover, add extra cheese if desired, and bake for an additional 15-20 minutes.

Let the stuffed onions rest for 10-15 minutes before serving.