In a large mixing bowl stir together 1-1/2 cups of the flour and the yeast. In a small saucepan heat the milk, sugar, cooking oil, and salt just until warm (120 degree F to 130 degree F). Add to the flour mixture. Then add the egg whites. Beat with an electric mixer on low speed for 30 seconds, scraping sides of bowl constantly. Beat on high speed for 3 minutes. Using a spoon, stir in as much of the remaining flour as you can.
On a lightly floured surface knead in enough of the remaining flour to make a moderately stiff dough that is smooth and elastic (6 to 8 minutes total). Shape into a ball. Place in a lightly greased bowl, turning once to grease the surface. Cover and let rise in a warm place until double (45 to 60 minutes). Punch dough down; turn out onto a lightly floured surface. Shape into 14 balls. Cover and let rest for 10 minutes.
Roll or pat each ball of dough into a 3-1/2-inch circle. Place filling in the center of each dough circles. (Use a scant 2 tablespoons savory filling or 1 tablespoon sweet filling.) Bring edges of dough up around filling, stretching dough until edges just meet; pinch to seal. Cover and let buns rest for 10 minutes.
Meanwhile, in a wok place a greased steamer rack over water. Bring water to boiling over high heat. Place buns, seam side down, on rack so the sides do not touch. (Cover and chill buns that dont fir on the rack.) Cover wok and steam buns for 15 to 17 minutes or until they spring back when touched. Repeat with remaining buns. Makes 14 side-dish servings.