Put 25g of flour and the water in a small pan and mix until smooth. Make sure there are no lumps in the mix before turning on the heat. Gently warm the flour paste over a low heat until it thickens, stirring constantly. You should see trails left by the spoon as you stir – be aware this process doesn’t take very long.
Add the remaining 300g flour and the rest of the dry ingredients to a large bowl, keeping the yeast and the salt at separate sides of the bowl. Mix one egg with the cooled tangzhong mixture and add to the dry ingredients along with the milk and melted butter. Mix well.
When all the ingredients are well mixed, tip the dough out on to a floured work surface and knead by hand. This dough is really sticky and you may need to add a little more flour to the work surface.
Knead the dough until it is no longer sticky and it begins to form a soft smooth skin. This will take around 10 minutes (a quick test is to lightly prod the dough, if it springs back it’s good to go!)
Transfer the dough to lightly oiled bowl. Cover and leave in a relatively warm place until doubled in size – about 1 hour.
Once the dough is risen, tip out on to a lightly floured surface and knock back the dough.
Divide the dough in to 3 equal (ish) pieces.
Roll one piece into an oval then fold one end of the dough halfway across, to the centre of the dough. Fold the other end on top until you have 3 layers. Gently roll the dough out again and then roll up, as you would to make a cinnamon swirl.
Repeat with the other pieces of dough then put all 3 pieces into a lightly oiled 2lb loaf tin. The seam of the roll should be on the base of the tin.
Cover with lightly oiled cling film and leave to rise again until the loaf is just reaching the top of the tin. Meanwhile preheat the oven to 175◦C
Brush the top of the dough with a beaten egg and then bake for approximately 30 minutes until golden brown. If it’s browning too fast cover with foil for the final minutes of baking.
Turn on to a cooling rack to cool before slicing.