Wash the swede under cold running water. Peel and slice then dice into even-sized cubes. Put in a saucepan and cover with plenty of freshly boiled, filtered water. Bring to the boil, cover, then lower the heat and simmer for 10-12 minutes or until tender.
Remove the swede from the pan and purée to a smooth texture in a blender of food processor, adding some of cooking liquid to get the right consistency. Allow the mixture to cool.