Soften yeast and 1 tablespoon sugar in lukewarm water. Set aside for from 10 to 15 minutes.
Mix together sugar, salt, and oil in a bowl. Add softened yeast. Add half of the flour and mix well.
Add remaining flour and continue mixing till well blended; knead on floured board until smooth.
Shape the dough into a ball and place in a greased bowl. Grease surface of dough. Let rise for from 30 to 40 minutes in a warm place.
Punch down dough, divide it into desired sizes, form into balls and let them rise again for 30 minutes.Flatten dough pieces. Spoon prepared sweet ground munggo or any desired filling into the center.
Seal dough and shape into small balls. Place a piece of clean paper at the bottom of the balls to prevent them from sticking to the steamer.
Let the balls rise for from 1 to 1 1/2 hours or until double in bulk. Steam for from 10 to 15 minutes. (Period of steaming depends on the size.). Yield: 1 dozen.