Skin the tomatoes and remove the seeds. Liquidise the flesh.
Mix together the tomato pulp, tomato purée, sugar, anchovy essence and fennel fern. Season with salt and black pepper. Fold in the cream and prawns and re-season to taste.
Place the mixture into small moulds and freeze for 3-4 hours.
The sorbet should be served half frozen, so turn onto plates a few minutes bef