Mix the ingredients for the yeast batter together in a large bowl. Cover and leave in a warm place for about 20 minutes until frothy.
Sift the flour and salt into a large bowl. Rub in the butter until the mix resembles fine breadcrumbs.
Add the sugar and stir in the yeast batter mixing well to form a soft dough. Turn the dough onto a lightly floured board and knead until smooth.
Shape the dough into a round ball, place in a covered greased bowl and leave in a warm place until doubled in size.
Put the risen dough into a larger bowl (if needed) and knead in the sultanas, working them through till evenly distributed. It feels like it's going to take forever but don't worry you will get there in the end.
The dough should be smooth. Place on a greased baking tray, cover and leave in a warm place for 1 hour.
Preheat oven to 180 degrees C.
When its ready to bake, make sure that there are no cracks visible in the dough, especially on top!
Brush with a beaten egg and bake for 50 minutes or until a skewer comes out clean. Best of luck!