Preheat your oven to 200C (400F). Cut the onions in half lengthwise. Remove any papery skins that are easy to discard but don’t worry about peeling.

Place onions cut side up on a roasting tray. Drizzle generously with oil and roast until well browned and soft – about 45 minutes.

When the onions are soft allow to cool for a few minutes before slipping them out of their skins. Slice cooked onion and place in a medium saucepan.

Add wine or vinegar and simmer for a few minutes before adding the stock. Bring to the boil then simmer for 5-10 minutes.

Taste and season generously with salt and pepper. Serve in deep bowls with parmesan grated over.