Mix the salt, egg whites and 25 ml (¾ fl oz) water together to make a bound mixture. Take the turnip and completely encase it in the salt mix. Put the turnip on a tray and bake in a 180°C (35°F) oven for about 35 minutes, or until cooked through with minimal resistance to a skewer. Remove from the salt crust and leave to cool. Thinly slice with a mandolin or sharp knife.