Peel the onions. Cut a small slice from the top. Cut a small slice from the bottom. This helps them sit flat. Boil them in water. Boil for 15 minutes. They should be tender. Let them cool. Scoop out the centers. Leave 2-3 outer layers. Chop the scooped onion.
Make the Stuffing
Melt butter in a pan. Cook the chopped onion. Cook until soft. In a bowl, mix pork. Add breadcrumbs. Add milk and egg. Add parsley. Season with salt and pepper. Add cooked onion. Mix well.
Stuff the Onions
Fill each onion. Use the pork mixture. Press it in firmly. Don't overfill.
Bake the Onions
Place stuffed onions. Put them in a baking dish. Pour in broth. Add white wine. Add bay leaf and thyme. Cover with foil. Bake at 350°F (175°C). Bake for 45 minutes. Remove foil. Bake for 15 more minutes. Brown the tops.