Combine the flour and the milk for the tangzhong in a small saucepan. Place this over medium heat and whisk constantly until the mixture is cooked into a thick and glutinous paste.

Remove it from the heat and scrape it into a small bowl. Let it cool down until just lukewarm to the touch.

While the tangzhong is cooling, combine the warm milk, sugar and yeast in the bowl of a stand mixer. If using active dry yeast, let this sit for around 5-10 minutes until it becomes foamy, if using instant yeast this step can be skipped.

Add in the cooled tangzhong, the dough flour, egg and salt. Turn the mixture onto low speed and combine it into a shaggy dough.

Turn the mixer to medium speed and mix for 5 minutes until the dough gains some strength.

Add in the softened butter a few cubes at a time and continue kneading for a further 12-15 minutes until the sticky dough is strong and pulls away from the sides of the bowl.

Let the dough rest for 5 minutes, then break off a piece and see if it can stretch out really thin without tearing. This is called the windowpane test and is a good way to see that the gluten has developed enough.

Add the dough to a lightly greased bowl and cover it with plastic wrap, a damp kitchen towel or a lid.

Let the dough rise in a warm place until doubled in size, around about 1 - 1 1/2 hours. The exact rise time will depend on your room temperature.

Punch down the dough and pull it from the bowl onto a floured work surface. Weight the dough, then cut it into 3 equal pieces. Use a scale to get really equal proportions. Shape each piece into a ball, using a little flour on your hands and the tops of the dough to stop them from sticking.

Use a rolling pin to roll each dough ball on the work surface into a long oval shape, around 20cm/8-inches in length. Roll up each piece like a swiss roll. Place each roll into a parchment paper-lined 9x5 inch loaf pan.

Cover the baking pan with compostable plastic wrap or place it in a warm place to rise again until doubled in size.

Preheat the oven to 350°F/180°C

Mix together an egg with a tablespoon of water and brush the top of the dough with this egg wash.

Bake the bread in the preheated oven for around 30-35 minutes until deep golden brown on top. If you find the bread is browning too quickly, loosely cover it with aluminium foil.

When you remove the bread from the pan and tap the bottom of it, it should sound hollow. The internal temperature of the loaf should be around 200°F/94°C.

Let it cool on a wire rack.