- With a paring knife, remove the tops of the onions. Make several X-shaped incisions in the centre of the onions and core with a spoon to keep only the two outer layers. Use a knife if necessary. Finely chop 500 ml (2 cups) of the onion pieces.
- In a large pot of salted boiling water, blanch the cored onions for 5 minutes. Drain and set aside.
- With the rack in the middle position, preheat the oven to 180 °C (350 °F).
- In a skillet, brown the chopped onion and garlic in the oil. Remove half the mixture and set aside in a bowl. Add the ground beef to the skillet and cook thoroughly. Add the wine or broth and Worcestershire sauce. Reduce by half. Season with salt and pepper. Pour into a bowl and allow to cool. Add the bread cubes, egg and parsley. Adjust the seasoning. Stuff the onions with this mixture.
- In the same skillet, add the reserved onion mixture. Add the tomatoes, sugar and basil. Bring to a boil and simmer for 5 minutes, uncovered. Season with salt and pepper.
- Pour the sauce into a 25 x 20-cm (10 x 8-inch) baking dish. Place the stuffed onions over the sauce and cover with aluminum foil. Bake for about 1 hour, remove the foil and bake for an additional 15 minutes.