Sift flour, sugar and salt. Dissolve the yeast in lukewarm water, add flour mixture slowly and mix well until smooth. Knead well and put dough in a bowl. Place wet cloth over dough and let rise until dough has risen 2 1/2 times. Knead with butter for 20 minutes.
Niku (Meat Stuffing):
1 1/2 lbs. ground pork
5 or 6 shiitake, pre-soaked and cut up fine
2 bamboo shoots, cut up fine
5 or 6 scallions, chopped fine
1 small piece fresh ginger, grated
1 small clove garlic, minced
3 Tbsp. shoyu(soy sauce)
1 Tbsp. sake
2 tsp. sugar
1 Tbsp. cornstarch
Put oil in pan and heat. Add minced garlic, ginger and pork and cook well. After pork has changed color, add vegetables and seasonings. Sprinkle cornstarch over mixture. Divide dough into 20 balls and make flat rounds. Place meat mixture in center and shape into round balls.
Put a piece of wax paper on each ball. Place wet cloth on bottom steamer to prevent sticking. Steam 10 or 15 minutes. Serve with shoyu and mustard.