Preheat the oven to 325°F (165°C). In a 9-inch (23-centimeter) square baking dish or roasting pan, combine the pork, garlic, pepper, oil, salt, and white pepper. Toss to coat evenly. Cover the baking dish with foil and roast for 1½ hours.

Remove the pork from the oven, reserve ¼ cup of the juices and drain the rest.

In a 2 cup (480 milliliter) liquid measuring cup whisk together honey, soy sauce, hoisin sauce, oyster sauce, Shaoxing wine, brown sugar, sesame oil, and five-spice powder. Pour over the pork in the pan along with the reserved juices and toss to coat. Re-cover the pan with foil and roast for 1 hour longer, until the pork is cooked through, about half of the sauce has been absorbed, and the meat is tender and easily shreddable.

Remove the foil. Using two forks, shred the pork and mix. The sauce left in the pan will absorb into the meat as it sets.

Allow the carnitas to cool in the pan at room temperature for 1 hour, then refrigerate for at least 1 hour.

In a small pot, add the milk, ¼ cup (60 milliliters) of water, and the bread flour and whisk to combine. Bring to a boil over medium-high heat and continue whisking until a thick paste forms, about 1 minute. Transfer the tang zhong to a small bowl and let cool to room temperature.

In the bowl of a stand mixer fitted with the dough hook attachment, add the bread flour, ¼ cup (90 grams) of the tang zhong (discard the rest), the sugar, eggs, cream, milk, milk powder, yeast, and salt. Mix on low speed for 3 minutes, then increase the speed to medium and mix for an additional 7 minutes.

With the mixer running, add the butter several cubes at a time, allowing the dough to come back together before adding more. Once all the butter has been added, continue to mix on medium speed until the butter is fully incorporated, 2 minutes more. The dough will be sticky.

Grease a large bowl with nonstick spray or vegetable oil. Place the dough into the bowl and cover with a tea towel. Let it proof until doubled in size, 1½ to 2 hours.

Punch the dough down and turn it out onto a lightly floured work surface. Flatten the dough with your hands to release any remaining air bubbles.

Line two 13x17-inch (33x43-centimeter) baking sheets with parchment paper. Portion out the dough into twelve equal (50 grams) pieces. Lightly dust your work surface with flour. Take one portion of the dough and flatten it using the palm of your hand. Add a heaping tablespoon or two of carnitas to the center of the dough. Fold all the edges inward and pinch shut; it should loosely resemble a dumpling. Turn it seam-side down onto your work surface and roll into a tight ball. Repeat with the remaining dough pieces, placing six buns on each sheet. Cover each sheet loosely with a tea towel and let them proof until doubled in size, about 1 hour.

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and sugar. Mix on low speed, moving up to medium speed until light and fluffy, about 2 minutes.

Scrape down the sides and bottom of the bowl and add the egg yolks one at a time, allowing the mixture to come back together before adding the next. Scrape down the sides of the bowl and mix on medium speed until fully incorporated, about 1 minute.

Scrape down the bowl again and add the flour, custard powder, baking powder, and salt. Mix until it just comes together into a shaggy ball of dough, about 30 seconds.

Divide the dough in half and place one portion in between two sheets of parchment paper measuring roughly 12x16 inches (30.5x40.5 centimeters) each. Roll out the dough into a thin layer, ⅛-inch (3 millimeters) thick, mimicking the shape of the parchment. Place the sheet of rolled dough onto a baking sheet and refrigerate until ready to use. Repeat with the other portion.

Preheat the oven to 375°F (190°C) and make the egg wash. In a small bowl, add the egg, the egg yolks, milk, and salt, and whisk until smooth. Pour through a fine-mesh sieve to strain out the solid bits.

Remove the sheets of bolo dough from the refrigerator, peel off one piece of parchment paper, gently lay it back onto the dough, flip the whole thing onto your work surface, and peel off the other piece of parchment. Use a 3½-inch (9-centimeter) circle cookie cutter to cut out twelve discs. Save the scraps and reroll them between two sheets of parchment paper to cut more discs. Repeat until the dough runs out.

Egg wash the tops of the buns and the bolo discs. Place one disc on top of each bun and bake until golden brown, 25 to 30 minutes, rotating halfway through baking. Allow the buns to cool on the baking sheets or on wire racks.