Slice the leek (green part too), then gently sauté under cover in the olive oil until soft. This should take 8-10 minutes.
Meanwhile, peel the potatoes & parsnips, then cut them into 2 cm pieces. Roughly chop the broccoli florets and dice its stalk. Mince the garlic.
When the leek has softened, add the garlic, stir for a few seconds, then add the potatoes and broccoli stalk pieces. Sauté (under cover) for 5 minutes, then add the stock, bay leaf and broccoli florets.
Bring to the boil and cook for about 10-25 minutes, until the vegetables are tender.
Turn off the heat. Discard the bayleaf and add the parsley leaves. Liquidise the soup in a food processor or using a stick blender.
Serve it with freshly ground pepper and freshly squeezed lemon juice.