Preheat your oven to 425 °F.
Fill a large pot with water and set to high heat while you prepare the onions.
Slice the top and bottom off of the onions and remove the peel.Using a sharp knife slice the onion halfway (lengthwise) through the layers, cutting until you hit the middle of the onion. This will make a slit in the onion, making it easier (once boiled) to peel back its layers. Once the water is boiling, add the onions, and allow them to simmer for 10-15 minutes. You want to be able to easily peal back its layers, but avoid over-cooking.
Remove the onions from the water, add to a colander and allow to cool for 15-20 minutes while you prepare the filling.
To a large frying pan, add the olive oil and set to medium heat.
Add the garlic, shallot, ground beef and Italian sausage and begin to fry, breaking up the meat into small pieces with a wooden spoon.
Once the meat is nearly cooked and browned, add the salt, pepper, crushed fennel seeds, dried basil, dried oregano, onion powder, and red pepper flakes and let cook for an additional minute.
Next, add the rinsed rice, fresh thyme, can of finely chopped tomatoes and chicken broth.
Allow the mixture to cook on medium heat, stirring often, just until the broth is absorbed and the rice is slightly cooked. About 6-7 minutes.*Don't worry about fully cooking the rice, it will finish cooking in the oven.Remove the pan from the heat and mix in the Italian parsley. Next, prepare the sauce by mixing together the strained tomatos, chicken broth and salt. *Depending if you use a salted chicken broth will determine if you need to add more salt, so taste the tomato sauce before adding it to the onions. To a large oven safe pan, or deep baking dish add a thin layer of the tomato sauce to the bottom of the pan.
Next, begin to stuff the onions.Take each onion layer, add about 2 tbsp of the meat mixture to the centre and gently roll, ensuring the filling stays in tact.Add the onions seam side down into the prepared pan or baking dish and ensure the onions fit snug.Repeat until all onions have been used. Pour over the remaining tomato sauce, cover with foil and bake for 30-35 minutes, remove the foil and continue cooking for another 20-30 minutes or until slightly golden and bubbly. The onions should be very soft and slightly caramelized.Sammy's tip: I like to broil the onions during the last 2 minutes of cook time. Remove the onions from the oven and allow to cool for 10 minutes.
Finish with balsamic glaze, a drizzle of olive oil and more fresh parsley.