Whisk the ingredients together in a small saucepan.

Place the saucepan over low heat.

Keep whisking until the ingredients form a thick paste. The consistency should be thick enough so that as you whisk the mixture, the whisk leaves lines in the mixture which remains.

Remove the paste to a small bowl, and set it aside to cool down.

Measure the flour, yeast, salt and sugar into the bowl of an electric stand mixer.

Mix the dry ingredients together using a dough hook.

Add the cooled Tangzhong.

Slowly add the milk until the mixture comes together into a sticky dough.

Add the butter, one tablespoon at a time. Wait for each tablespoon of butter to be fully incorporated into the dough before adding the next.

Continue kneading the dough on medium speed for about 10-15 minutes, or until the dough passes the windowpane test. (See Kitchen Notes below). By this stage, the dough should also be coming away from the sides of the bowl.

Lightly oil a large, clean mixing bowl.

Roll the dough into a smooth ball and place it into the mixing bowl.

Cover the dough with a clean tea towel or bowl cover, and place it somewhere warm for about 1.5 hours, or until it has doubled in size.

Gently remove the dough from the bowl. The dough will deflate as you handle it.

Divide the dough into 9 equal portions. Use a digital scale for even-sized buns.

Roll each piece of dough into a smooth ball. I do this by pinching the seams together into a ball, and then rolling the dough on the kitchen bench while cupping it with your hand to ensure that the dough is smooth on all sides.

Place the smooth balls of dough onto a large baking pan lined with baking paper.

Place the baking pan somewhere warm for about 20 minutes, or until the buns have puffed up slightly.

The filling is simply the salted butter.

Cut small blocks of cold salted butter, about 10 g/0.35 oz each. The length of the butter should be about 5 cm/2 inches, small enough to wrap inside the dough later.

Take one piece of dough.

Gently roll the dough into a long log.

Use a small rolling pin to flatten the dough, trying to form a very long triangle as you do so. The length of the dough should be about 50 cm/20 inches. The wider end of the dough should be wide enough to fit a small piece of butter, about 6 cm/2.5 inches wide.

Place the piece of butter at the wide end of the dough, and slowly wrap the butter in the dough, pinching the sides to secure the piece of butter. Keep rolling until you reach the end of the dough.

Once the dough is all rolled up, it should look like a croissant.

Place the dough with the seam facing down on a large baking tray lined with baking paper.

Repeat the above steps with the remaining pieces of dough.

Place the pan somewhere warm, covered with a clean tea towel, for about 20-30 minutes, or until the buns have puffed up slightly.

Place a metal baking tray on the middle shelf.

Place a small roasting pan or cast iron pan on the lowest shelf.

Put the kettle on to boil some water.

Spray the buns with some water.

Sprinkle the middle of the buns with some coarse sea salt.

Place the tray of buns onto the middle shelf.

Quickly pour the boiling water into the tray or pan on the lowest shelf. This will immediately create some steam, which you want to trap in the oven, so close the oven door ASAP.

Bake the buns for about 10 minutes.

Reduce the heat to 180°C/356°F.

Bake the buns for another 10 minutes. If the buns are browning too quickly, cover the buns with a loose sheet of foil for the remaining baking time.

The buns are cooked if an internal thermometer reads 85°C/185°F.

Some butter will have melted from the buns onto the baking tray, and this is completely normal. The melted butter will help to crisp up the bottom of the buns.

Leave the buns in the pan for about 5 minutes, before carefully removing the buns to a wire rack to cool completely.