Make a dough first. Blend together 2½-oz strong flour, the half teaspoon sugar, and the yeast and milk to make a thick batter. Leave the batter in a warm place until frothy, for about twenty minutes. Sift the remaining strong flour and salt, and rub in the l oz butter. Add this flour mixture to the batter, and mix well to give a fairly soft dough. Knead for about ten minutes. Place in a lightly oiled polythene bag and allow to rise until double in size. Turn the dough on to a lightly floured surface and knead. Butter an eight-eight and a half inch loose-bottomed, springform tin (about four pint capacity). Line with the dough.
For the filling, whisk the egg whites stiffly, gradually adding the caster sugar. Sieve the cheese and add a little of the egg white to it. Fold the mixture into the bulk of the egg whites with a pinch of salt, the flour added a spoonful at a time, the egg yolks, melted butter and raisins. Turn into the tin and bake in the bottom of the oven heated to 350°F, 180°C, gas mark 4 for about three quarters of an hour. Allow to cool, remove from the tin, and dust heavily with icing sugar.