Tangzhong Starter:

In a small saucepan, add in 3 tbsp of bread flour, and 1/4 cup of water, and whisk till the flour has dissolved and there are no more lumps. And in 1/4 cup of whole milk. Continue to whisk together to combine.

Set over low heat, stirring constantly with a spoon, for 3 to 5 minutes.

After 3 to 5 minutes of whisking over low heat, it should look like a thick paste but still pourable. It's done when the spoon starts to leave tracks on the bottom of the pot when stirring.

Turn off the heat and transfer the tangzhong starter into a small heatproof bowl, cover with plastic wrap touching the tangzhong to prevent a skin from forming, and let it come to room temperature. The starter will continue to firm up as it cools.

Dough:

Take 1 large egg and 4 tbsp of unsalted butter, and leave them on the counter to come to room temperature. Cut the butter into 4 pieces.

In a microwavable bowl, microwave 1/2 cup of whole milk till it is scalding, about 1 1/2 min in the microwave, to a minimum of 180 F (80 C). This deactivates the whey proteins in the milk, which may hinder gluten development. While it's hot, whisk 1 tbsp of granulated sugar into the milk.

Let the milk cool down by whisking it constantly, till it reaches 105 to 115 F (40-46C). When the milk is 105-115 F, whisk in 1 envelope (which is 1/4 oz or 2 1/4 tsp) of active dry yeast till it gets dissolved and let it proof for about 10 minutes. It should start to look foamy on top. If it does not get foamy, it means your yeast is not working. Start again with new yeast.

In the bowl of your stand-mixer, add in 2 1/2 cups of all-purpose flour, 2 tbsp nonfat powdered milk, 3 tbsp of granulated sugar, and 1 tsp salt. Using the regular beater attachment, mix this on medium-low speed to combine the dry ingredients. Stop the mixer, and add in the 1 large room temperature egg, the yeast-milk mixture, and the tangzhong mixture. Mix this together on low speed just until the ingredients are combined. With a spatula, scrape the batter from the sides of the bowl and off of the beater and remove the beater attachment and cover loosely with plastic wrap. Let the mixture rest for 5 minutes - this will allow the flour to soak up the liquid.

Attach the dough hook attachment, and knead on low speed (level 3) for 5 minutes.

After 5 minutes of kneading on low speed, add in the pieces of room temperature unsalted butter (4 tbsp total) one piece at a time, waiting for the butter to get incorporated before adding in the next piece, about 30 seconds to 1 minute between each addition of butter.

Once all the butter has been added, turn the speed up to medium (level 5), and continue kneading the dough for another 5 minutes, till the dough is smooth, springy, and no longer sticks to the side of the bowl.

Take a large bowl, oil it very well, and transfer the resulting dough into the oiled bowl. Cover the dough with plastic wrap, and let it sit for 1 1/2 to 2 hours. This will allow it to rise and puff up (1st proof).

Assembling the Pork Floss Buns:

Take a large sheet pan, and line it with parchment paper.

In a small bowl, add in 1/3 cup of kewpie mayonnaise and 2 tbsp of condensed milk till they are well combined. Have 2 cups of pork floss ready in a bowl.

Punch down the dough, and turn it onto a smooth clean surface, roll it into a long tube, and divide it into 10 approximately equal pieces, estimating by eye and weight in your hands.

Form the dough into tight spheres by rolling each piece in your palms with cupped hands - do this for all 10 pieces. This ensures that there are no air bubbles in the dough. Then set them aside to rest under plastic wrap to prevent them from drying out.

Then take 1 sphere at a time, and use a rolling pin to flatten each sphere into a circular disc shape that's about 4 inches in diameter. The thickness of the dough should taper towards the edges of the circle - i.e. the disc should be thicker in the center and thinner around the edges.

Add about 1 tsp of the kewpie mayo mixture to the middle of the mixture, spreading it out a bit, then add 1 tbsp of pork floss on top. Fold the disc together by bringing the opposite sides of the circle together, and then pinching the closed circle together tightly, then twisting the top, to ensure the bun is sealed.

Invert the bun placing it seam-side down on the prepared parchment paper-lined sheet pan. And shape it with your hands as necessary to create a more even circular shape.

Repeat this with the other 9 pieces of dough and kewpie mayo mixture and pork floss. Cover the formed buns with plastic wrap as you're forming the remaining buns, to prevent the formed buns from drying out. Once all the buns are formed, keep them covered loosely with plastic wrap, and let them rise again until they are doubled in size, about 1 hour (2nd proof). Keep the remaining kewpie mayo mixture in the fridge, which will be used later for the topping. The pork floss can be kept at room temperature.

Preheat your oven to 350 F (175 C) about 15 minutes before the end of the 2nd proof. In a small bowl, prepare an egg wash by whisking 1 egg and 1 tbsp of water till they are well combined.

Brush the top of the risen buns with egg wash. Bake in the preheated oven at 350 F (175 C) for 15 to 17 minutes, or until the tops are golden brown. If you have a thermometer, buns are done when they read 185 - 190 degrees F (85 - 88 C) in the middle of each bun. When the inside goes past 200 degrees F (93 C), the buns will start becoming a little dry.

Once out of the oven, let them cool slightly, about 5 minutes, then transfer them onto a cooling rack.

When the buns have cooled completely (after cooling on the racks for an additional 30 minutes or so), only dress the buns you're serving immediately. Brush the top of each bun with a light layer of the prepared kewpie mayo mixture. Invert and press the top of the bun (the part covered with kewpie mayo mixture) into the bowl of pork floss, to get a light layer of pork floss on top. Repeat this with all the buns you are serving immediately. Enjoy!

Store the remaining (undressed) buns in an airtight container - they will keep at room temperature for 3 to 5 days. Store remaining kewpie mayo sauce in the fridge. Commercially-bought pork floss does not need to be refrigerated. Just store it in an airtight container.