Heat the oil in large pan. Add the leeks and onion and fry on a very low heat for 10 minutes, until softened, stirring now and then to stop them catching.
Add the artichokes, stock, bay leaf and rosemary and season with the grated nutmeg and salt and pepper. Bring to the boil, reduce the heat and simmer for 25–30 minutes, until the artichokes are very soft.
Remove the bay leaf a