This is made in a food processor, which gives a smooth, light, delicate purée.
Put the swede and ginger in a saucepan, cover with cold water and add a little salt. Bring to the boil and simmer for about 20 minutes, until tender. Leave to drain thoroughly in a colander for several minutes, then transfer to a food processor. Add the butter, orange juice and zest and process for a few seconds. Transfer to a bowl and mix in the cream and some seasoning.