Nigel Slater's recipe for chicken and mushroom casserole, plus a mint and kefir ice

A cosy winter dinner is best finished with a refreshing mint ice The weather has been bitterly cold all week and the heating in this house is, to say the least, unpredictable. On the coldest day, with the wind howling down the chimneys, I made an old-fashioned chicken casserole, the mushroom-laden sauce deepened with sherry and pancetta. To swirl into the dark and aromatic juices on our plates, I made a purée of parsnips, the smooth and buttery kind rather than my usual rough mash. We thawed ou...