In a small saucepan, whisk together 20g bread flour with 100ml water until smooth. Put over a low-medium heat and cook, stirring constantly, until a thick paste. This happens fast, around 5 mins. Remove from heat and set aside to cool to room temperature.

In a large bowl, or the bowl of a stand mixer, combine 250g bread flour with the yeast, sugar and salt. Keep the yeast and salt on opposite sides of the bowl so the salt doesn't touch the yeast directly.

Add the cooled yukone, warm milk and beaten egg. Mix (by hand or with a dough hook) for about 2 mins until it comes together into a rough dough.

Knead the dough until smooth and elastic, around 8 mins in the mixer. Add the softened butter a little at a time and continue kneading for another 8-10 mins until the dough is soft, glossy and you can stretch a small piece thin enough to see light through it without tearing.

Shape the dough into a ball, put in a lightly oiled bowl, cover with a damp towel and leave in a warm place to rise until doubled in size, around 1 hr 30 mins.

Punch down the dough and divide into three equal pieces. Roll each piece on a lightly floured surface into an oval, fold the sides in, then roll up from the bottom into a tight cylinder. Put all three pieces seam-side down side by side into an oiled shokupan or 900g loaf tin.

Cover the tin loosely and leave in a warm place until the dough rises to about 80-90 per cent of the tin's height, around 1 hr. If using a lidded shokupan tin, close the lid once it's close to full.

Heat the oven to 180C/160C fan/gas 4. If not using a lidded tin, brush the top of the loaf with the milk or melted butter. Bake for about 20 mins until deep golden brown, then drop the heat to 170C/150C fan/gas 3 and bake for another 5-10 mins until the loaf sounds hollow when tapped on the base. Turn the loaf out of the tin immediately and cool on a wire rack for at least 30 minutes before slicing. Will keep wrapped for up to three days (see tip).