Add flour, sugar, and yeast to a large bowl and mix well. Gradually pour in the warm water while stirring with chopsticks or a spoon until a shaggy dough forms. Knead by hand until smooth and soft. No need to knead until stretchy—just smooth and even.

Divide the dough into 12 equal portions (about 100–110g each). Roll each portion into a smooth ball and cover to prevent drying.

Roll one dough ball into a round wrapper with a thicker center and thinner edges. Add about 30–35g red bean paste to the center. Gently pleat and seal the top, shaping into a round or oval bun.

Place the buns on parchment paper or a steaming cloth, leaving space between each. Cover and let them rest until noticeably puffy and spring back when gently pressed.

Bring water to a full boil, then place the buns in the steamer. Steam over medium heat for 15 minutes. Turn off the heat and let them rest inside the steamer for 3 minutes before opening the lid.

Remove from the steamer and enjoy warm. The buns should be soft, fluffy, and generously filled.