In a bowl, mix the all-purpose flour and sugar. Dissolve the yeast in the warm water, then pour it into the flour mixture. Knead into a dough (add a little oil if it's too sticky). Cover the dough with plastic wrap and let it rest for 30 minutes.

Uncover the dough and knead it into a log. Divide into five equal pieces.

Mash the steamed sweet potato. Flatten each dough piece and fill with the mashed sweet potato.

After shaping the buns, place them in a steamer basket. Put the basket in an electric rice cooker and let the buns rest for 1 hour before steaming.

Add about 1 2/3 cups water (400 ml) to the outer pot. Steam for about 30 minutes. Remove and enjoy. Store leftovers in the refrigerator and reheat by steaming or microwaving when ready to eat.