Buns: Mix warm water with sugar to dissolve. Add yeast and let stand for 10 minutes. Mixture should get foamy, or the yeast is dead. Mix in lard.
In a food processor, add flour and yeast mixture. While blade is spinning, pour in water until a ball forms. If dough is too sticky, add more flour. If dough appears dry and doesn't form a ball, add more water. As soon as a ball forms, take dough out and knead by hand on a floured surface. For 10 minutes roll dough into one long log about 2-inches thick. Cut into 2-inch pieces.
Filling: In a saute pan coated with oil, saute garlic and ginger. Add shiitakes and cook until soft. Season with salt and pepper. Let mixture cool.
Assembly: In a bowl, mix shiitakes, chicken, chives, and truffle oil. Season with salt and pepper. Keep filling chilled before stuffing buns.
Form thick circles and place about 1 tablespoon of stuffing in the middle of each piece of dough. Encircle stuffing with the dough, but do not seal. Let rest in a warm place for 30 minutes.
In a steamer basket, steam buns for 10 to 12 minutes.