Strain through a fine sieve. Set aside 100ml/3½fl oz to make the pea purée and the remaining 500ml/18fl oz to make the risotto. (Add water to make the volume up to 500ml/18fl oz if necessary.) ...

Add a knob of butter and melt into the risotto to give a silky texture. Just before serving, stir in the pea and leek puree and the parmesan cheese and warm through. Season with pepper.