Makes 12
Dough:
4 tablespoons sugar
1/2 cup warm milk (110oF)
1/3 cup warm water (110oF)
2 teaspoons active dry yeast
About 2-1/2 cups flour
1/2 teaspoon salt
Filling:
8 dried black mushrooms
2 tablespoons cooking oil
1/2 cup minced green onions
2 teaspoons minced garlic
1/2 cup water
4 teaspoons hoisin sauce
4 teaspoons oyster-flavored sauce
1 tablespoon sugar
2 teaspoons cornstarch dissolved in 2 tablespoons water
1-1/2 cups chopped Chinese Barbecued Pork
1 egg yolk, lightly beaten
Dissolve 2 tablespoons of the sugar in milk and water. Sprinkle in yeast; let stand in a warm place until bubbly, about 10 minutes. Gradually mix in remaining 2 tablespoons sugar, 2 cups flour, and salt. Add more flour as needed until dough is no longer sticky. Place dough on a lightly floured board and knead until smooth and elastic, 6 to 8 minutes. Place in an oiled bowl, cover, and let rise in a warm place until doubled in bulk, about 1 hour.
Meanwhile prepare filling:
Soak mushrooms in warm water to cover until softened, about 20 minutes; drain. Discard stems and coarsely chop caps. Heat a wok over high heat. Add oil, swirling to coat sides. Add green onions, garlic, and mushrooms; stirfry for 1 minute. Stir in water, hoisin sauce, oyster sauce, and sugar. Add cornstarch solution and stir until sauce boils and thickens. Stir in pork. Cool.
Cooking:
Punch down dough, then roll into a cylinder. Cut cylinder into 12 equal pieces. Roll each into a ball; cover. Flatten each ball and roll into a circle 4 to 6 inches in diameter. Place 1 heaping tablespoon filling in center. Gather edges of circle over filling; twist and pinch edges together to seal. Place buns, seam side down, 2 inches apart on an oiled baking sheet. Cover and let rise in a warm place until puffy and light. Brush tops with egg yolk.
Preheat oven to 350oF. Bake buns until golden brown, 18 to 20 minutes.