Finely chop one onion and garlic cloves.
Heat some olive oil in a pot, then gently sauté the onion for 8 minutes over low heat.
Add the garlic and half of the thyme (leaves only).
Meanwhile, peel the parsnips, then chop them into small chunks.
When the onion has softened and lightly browned, add the parsnips and stir through. Add enough stock to cover the vegetables, then bring to the boil, add the bay leaf and turn down the heat. Gently simmer for about 25 minutes, until the parsnip has softened.
Remove the bay leaf. Using a stick blender, process the soup until you get a creamy consistency.
Add more stock, if you think it’s too thick.
Slice the other onion into very thin rings.
Heat some olive oil in a frying pan, and gently fry the onion until soft and brown. Add the balsamic vinegar and thyme and stir for a couple of minutes or until the onion has caramelized.
Serve the soup warm with a dollop of yoghurt or a spoonful of apple cider vinegar, topped with the caramelised onion.