1. Cut the apples into chunks and put them into a saucepan. Add the sugar and just a little water, and cook very gently until the apples are flopsy like snow. They will take about 15 minutes.
2. Separate the egg and beat the white until really thick. (You do not need the yolk.) Add a pinch of salt and the white will get even thicker.
3. It is stiff enough when it passes the upside-down test.
4. When the apples have cooled, fold in the egg white gently, then the yoghurt.
5. Spoon into individual dishes, and put in the fridge for ardour or so until set.