For the Tangzhong: In a microwave-safe bowl, combine 40g bread flour and 255mL milk. Whisk until combined. Microwave in 30-second increments, whisking vigorously between each, until a pudding-like consistency forms.

Add 56g cold unsalted butter to the hot Tangzhong and stir until melted. Add 1 egg, 50g sugar, 14g milk powder (optional), and 6g salt. Stir to combine.

Transfer the mixture to a stand mixer bowl and let cool for 5 minutes, whisking occasionally. Once cooled to tepid bath water temperature (max 85F), add 350g bread flour and 8g instant yeast.

Using the dough hook, mix on low speed until flour is moistened, then increase to medium-high speed (6 on KitchenAid) for 5 minutes. Scrape down the bowl as needed.

Continue mixing on medium-low speed (4 on KitchenAid) for another 3-5 minutes until the dough is smooth and elastic, able to stretch into a thin translucent film.

Knead by hand for 10-15 minutes if not using a stand mixer.

Shape the dough into a ball, oil a clean bowl, place the dough ball in the bowl smooth side up, cover, and let proof until doubled in size (45-90 minutes).

For the Chinese BBQ Marinade: In a bowl, combine 60g honey, 20g hoisin sauce, ¼ tsp Chinese five spice, ⅛ tsp white pepper, 2 minced garlic cloves, ¼ tsp sesame oil, 1 tbsp Shaoxing wine (or 1-½ tsp soy sauce), 1 tbsp light soy sauce, and ½ tsp dark soy sauce. Stir to combine.

For the Meat Filling: Cut 1 lb pork shoulder or chicken thighs into ½ inch thick slices. Pound with the back of a knife to tenderize and create surface area. In a separate small bowl, dissolve ¼ tsp baking soda and 1 tbsp water, add ½ tsp salt, and massage into the meat. Let sit for 1 minute.

Add the Chinese BBQ marinade to the meat and massage thoroughly until mostly absorbed (2-3 minutes). Mix in 1 tbsp cornstarch and 1 tbsp neutral oil. Let marinate for 5-10 minutes.

Heat a non-stick skillet over medium-high heat with a touch of oil. Add the meat in a single layer (cook in batches if necessary). Cook undisturbed until charred on the bottom. Flip and char the other side.

Add ¼ cup water, cover, reduce heat to medium, and steam for 2-3 minutes (3-4 minutes for chicken or thicker pieces). Remove lid, cook until water evaporates and meat is coated in a thick glaze. Ensure internal temperature reaches 165F. Dice the cooled meat.

For the Mushroom Filling: Soak 5-6 dried shiitake mushrooms in boiling water for 20-30 minutes. Wash and dice 1 lb fresh mushrooms. Remove woody stems from rehydrated dried mushrooms and dice the caps. Strain and reserve soaking liquid.

Heat a non-stick skillet over high heat with a touch of oil. Add fresh mushrooms, ½ tsp salt, and ¼ cup water. Cover and cook for 1 minute. Remove lid, cook until water evaporates. Add 1 tbsp oil and the diced dried mushrooms. Cook until browned, stirring occasionally.

Pour the Chinese BBQ marinade over the mushrooms. Lower heat to medium and cook until sauce is reduced and coating the mushrooms. Transfer to a bowl to cool.

For the Filling Base: Combine 15g cornstarch, 15g potato starch (or more cornstarch), and 50mL water. Stir until lump-free.

In a bowl, combine 20g honey, 1 tbsp light soy sauce, 1 tsp sesame oil, 1 tbsp hoisin sauce, ⅛ tsp white pepper, ¼ tsp Chinese five spice, ½ tsp chicken bouillon powder (or substitute), ¼ tsp dark soy sauce, and 150mL water or mushroom broth.

Dice ½ medium onion and mince 1" ginger. Heat 1 tbsp oil in the wiped-clean skillet over medium heat. Sauté onion and ginger until softened and lightly browned (about 5 minutes).

Add the sauce mixture to the skillet and bring to a boil for 1 minute. Stir the starch mixture and drizzle it in, stirring until a thick paste forms and turns translucent. Turn off heat, stir in 1 tbsp oil until smooth and glossy. Spread onto a tray to cool quickly.

Combine the cooled filling base with your chosen filling (pork, chicken, or mushroom). Cover and refrigerate.

Once the dough has doubled, flatten it to press out air. Shape into a ring, then into a log. Divide into 12 equal portions (about 60-65g each). Shape each portion into a smooth ball.

Roll out each dough ball to about 5 inches in diameter, making the edges thinner than the center. Flip the dough circle over (smooth side down).

Place a scoop of chilled filling in the center. Use the helical folding technique to crimp and seal the dough around the filling, forming a bun. Invert the bun so the seam is on the bottom. Gently roll with a cupped hand to round the shape.

Place shaped buns onto parchment-lined trays, leaving ample space between them. Cover with a damp towel or plastic wrap and proof in a warm place until almost doubled in size (30-60 minutes).

Preheat oven to 350F (175C) with racks in the top and bottom thirds.

Prepare egg wash by beating 1 egg with a splash of cream or milk.

Brush buns with a thin coating of egg wash. Let sit uncovered for 15 minutes to dry slightly.

Brush with a second thin coating of egg wash and sprinkle with sesame seeds (optional).

Bake for 18-20 minutes, or until golden brown all over. Swap trays top to bottom halfway through if baking two trays.

Let buns cool for at least 5-10 minutes before serving.