Gather all the ingredients. I highly encourage you to weigh your ingredients using a kitchen scale for this recipe.

Prepare one square piece of parchment paper for each bun you will make, about 3 x 3 inches (7.6 x 7.6 cm) for small buns. Set aside.

Put 2½ cups all-purpose flour, 2 scant Tbsp sugar, ½ tsp Diamond Crystal kosher salt, 1 tsp baking powder, 1 tsp instant yeast, and 1 Tbsp neutral oil in a large bowl. Slowly pour ⅔-¾ cup water into the bowl and mix until incorporated.

Lightly dust your hand with flour and knead the dough in the bowl until you can form it into a ball.

Transfer the dough onto a floured surface and knead for 10–15 minutes until smooth and silky.

Form the dough into a round shape, coat the bowl with oil, place the dough back in, cover with plastic wrap, and let it rise until doubled in size, about 30–60 minutes.

Soak 2 dried shiitake mushrooms in ½ cup water for 10–15 minutes.

Thinly slice 1 green onion and chop 4 leaves of green cabbage into 1-inch pieces. Sprinkle with 1 tsp salt.

Once the mushrooms are rehydrated, mince them and combine with ¾ lb ground pork, scallion, and squeezed cabbage.

Add 1½ tsp grated ginger, 1 tsp sugar, 1 Tbsp sake, 1 Tbsp soy sauce, 1 Tbsp toasted sesame oil, 1 Tbsp potato starch, and black pepper. Knead until well combined.

Once the dough has risen, divide it into 20 pieces and form each into a ball. Let them rest for 10 minutes.

Flatten each ball and roll into a round wrapper. Scoop 1½ Tbsp of filling into the center and seal the bun by pleating.

Place each bun on a parchment square, cover with plastic wrap, and let rest for 20 minutes.

Bring water to a boil in a large wok and steam the buns for 10 minutes.

Serve hot with soy sauce and Japanese karashi hot mustard.