In a large bowl, combine warm milk, sugar and yeast; let stand 5 minutes.
In a separate large bowl, sift flour, salt and sugar; add oil. Mix with a spatula until well incorporated. Knead until smooth and elastic, about 10 minutes. Place dough in a large bowl with oil, cover and let rise in a warm place, 1 hour.
In a large bowl, combine pork, fish sauce, soy sauce, white pepper, ginger and spring onions until evenly distributed. Divide dough into 10 equal portions. Roll each dough piece into a 5-inch round, 1/4 inch thick. Use a rolling pin to make the perimeter of the dough 1/8 inch thick.
Place 2 tablespoons of filling in the center of each dough circle. Bring up sides to cover filling and meet on top. Pinch and seal closed with a twist. Repeat procedure with remaining dough balls and filling.
In a steamer, arrange 5 buns seam side down, 1 inch apart. Cover with a lid wrapped in a kitchen towel.
Add water to a large skillet to a depth of 1 inch, and bring to a boil over medium-high heat. Place steamer in pan; steam 12 to 15 minutes.