Heat water or milk in the microwave for 30 seconds until it’s hot but not too hot to touch. Stir in the sugar, then sprinkle the yeast on top. Let it sit for 5 minutes until it becomes foamy. Once foamy, mix in the oil.
In a bowl, combine flour and baking powder. Mix the flour mixture into the yeast mixture and knead until a smooth, elastic dough forms. Let it rest for 1 hour.
Line your steamer with parchment paper and a steaming cloth or liner.
Transfer the dough to a work surface and divide into 10 equal pieces, about 44g each. Roll each piece into a ball, then flatten and roll out into a rectangle. Place a piece of Chinese sausage at one end, then make thin vertical cuts along the opposite edge. Press down the edges of the cuts to help seal.
Roll up each rectangle with the sausage inside and place the buns seam-side down in the lined steam basket. Cover and let proof for 30-60 minutes.
Add water to a pot, bring to a boil, then place the steam basket on top. Steam the buns for 10-12 minutes. Turn off the heat and let the buns sit, covered, for 5 minutes before serving.
Storage: You can freeze the buns once they have cooled. To reheat, just pop it back into the steam basket and repeat the steaming step.