Sieve flour and salt into a mixing bowl and rub in butter with your fingertips until mixture is smooth and free from lumps. Make a well in the centre.
Sprinkle yeast and sugar over lukewarm milk in a small mixing bowl; after a few minutes, stir well. Add vanilla extract, and strain into the centre of the dry ingredients. Gradually mix the dry ingredients from the sides of the bowl into the yeast mixture with your hands until a thick batter is formed. Cover the bowl and stand it in a warm place for about ¾ hour. Sprinkle with carefully washed and drained sultanas; mix all into a soft dough; turn out on a floured board and knead for a few minutes. Put the dough in a well-buttered and floured loaf tin and leave in a warm place to rise. When well risen, bake in a hot oven (450°-M7) until bread tests done.