In a stand mixer, combine 4 cups of all-purpose flour, 2 tablespoons of sugar, 2 teaspoons of instant yeast, and 1 teaspoon of baking powder. Gradually add 1½ cups of warm water (100-110°F) while mixing until a shaggy dough forms. Knead the dough on medium speed for 8 minutes, then switch to hand kneading for an additional 2 minutes until it becomes smooth and elastic.

Shape the kneaded dough into a ball and lightly brush it with oil to prevent drying. Transfer it to a large bowl, cover it with a damp cloth, and place it in a warm area. Allow the dough to rise for 1-2 hours, or until it has doubled in size.

Once the dough has risen, gently punch it down to release excess air. Divide the dough into 12 equal portions and roll each piece into a smooth ball. Flatten each ball into a disc to eliminate air bubbles, and then reshape them into smooth balls again. Place each bun on a square of parchment paper.

Arrange the shaped buns in a bamboo steamer, ensuring they have enough space to expand. Cover the steamer with a clean kitchen towel and let the buns proof for 30 minutes to 1.5 hours.

Prepare a pot of water by bringing it to a boil, then adjust the heat to medium-low. Place the bamboo steamer over the pot and steam the Mantou for 12 minutes without lifting the lid.

Carefully remove the steamed buns from the steamer using tongs. Serve the Mantou warm.