Heat a Tbspful of oil in a saucepan. Finely chop the onion and soften in the oil for about 5 minutes.
Meanwhile, peel and the potatoes, then add the onions.
Pour in the stock, bring to the boil and cook for about 10 minutes.
Meanwhile, roughly cut the broccoli (including stem). When the potatoes are tender but not cooked through yet, add the broccoli to the soup and cook for 5 minutes.
Turn off the heat and liquidise or blend the soup until smooth.
Add half of the cheese and blend again.
Serve with some grated nutmeg and the remaining cheese crumbled on top.