Heat the corn oil in a large saucepan. Working in batches if necessary, add the shallots and cook until evenly browned. Add the garlic, butter and thyme cook for another 2 minutes.
Pour in the stock and bring to a boil. Cover and simmer gently for 20-25 minutes or until the shallots are tender. Check regularly to ensure the stock has not evaporated. Season to taste.